Preliminary Pricing Supplement No. 15,766

Registration Statement Nos. 333-293641; 333-293641-01

Dated April 30, 2026

Filed pursuant to Rule 424(b)(2)

Morgan Stanley Finance LLC

Structured Investments

Dual Directional Buffered PLUS due May 31, 2030

Based on the Performance of the S&P 500® Index

Buffered Performance Leveraged Upside Securities℠

Fully and Unconditionally Guaranteed by Morgan Stanley

Principal at Risk Securities

￭The Dual Directional Buffered PLUS (the “securities”) are unsecured obligations of Morgan Stanley Finance LLC (“MSFL”) and are fully and unconditionally guaranteed by Morgan Stanley. The securities will pay no interest and have the terms described in the accompanying product supplement, index supplement, tax supplement and prospectus, as supplemented or modified by this document.

￭Payment at maturity. At maturity, if the final level is greater than the initial level, investors will receive the stated principal amount plus the leveraged upside payment, subject to the maximum upside payment at maturity. If the final level is equal to or less than the initial level but is greater than or equal to the buffer level, investors will receive at maturity the stated principal amount plus a positive return equal to (i) the absolute value of the percentage decline in the level of the underlier multiplied by (ii) the absolute return participation rate. If, however, the final level is less than the buffer level, investors will lose 1% for every 1% decline in the level of the underlier beyond the specified buffer amount. Under these circumstances, the payment at maturity will be less, and may be significantly less, than the stated principal amount of the securities, subject to the minimum payment at maturity.

￭The securities are for investors who seek a return based on the performance of the underlier and who are willing to risk their principal and forgo current income and returns above the maximum upside payment at maturity in exchange for the upside leverage feature, the absolute return participation feature and the buffer feature, each of which applies to a certain range of performance of the underlier over the term of the securities. Investors in the securities must be willing to accept the risk of losing a significant portion of their initial investment. The securities are notes issued as part of MSFL’s Series A Global Medium-Term Notes program.

￭All payments are subject to our credit risk. If we default on our obligations, you could lose some or all of your investment. These securities are not secured obligations and you will not have any security interest in, or otherwise have any access to, any underlying reference asset or assets.

TERMS
Issuer:	Morgan Stanley Finance LLC
Guarantor:	Morgan Stanley
Stated principal amount:	$1,000 per security
Issue price:	$1,000 per security (see “Commissions and issue price” below)
Aggregate principal amount:	$
Underlier:	S&P 500® Index‬‬ (the “underlying index”)
Strike date:	May 26, 2026
Pricing date:	May 26, 2026
Original issue date:	May 29, 2026
Observation date:	May 28, 2030, subject to postponement for non-trading days and certain market disruption events
Maturity date:	May 31, 2030
	Terms continued on the following page
Agent:	Morgan Stanley & Co. LLC (“MS & Co.”), an affiliate of MSFL and a wholly owned subsidiary of Morgan Stanley. See “Supplemental information regarding plan of distribution; conflicts of interest.”
Estimated value on the pricing date:	Approximately $947.70 per security, or within $45.00 of that estimate. See “Estimated Value of the Securities” on page 3.
Commissions and issue price:	Price to public	Agent’s commissions and fees(1)	Proceeds to us(2)
Per security	$1,000	$	$
Total	$	$	$

(1)Selected dealers and their financial advisors will collectively receive from the agent, MS & Co., a fixed sales commission of $ for each security they sell. See “Supplemental information regarding plan of distribution; conflicts of interest.” For additional information, see “Plan of Distribution (Conflicts of Interest)” in the accompanying product supplement.

(2)See “Use of Proceeds and Hedging” in the accompanying product supplement.

The securities involve risks not associated with an investment in ordinary debt securities. See “Risk Factors” beginning on page 6.

The Securities and Exchange Commission and state securities regulators have not approved or disapproved these securities, or determined if this document or the accompanying product supplement, index supplement, tax supplement and prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The securities are not deposits or savings accounts and are not insured by the Federal Deposit Insurance Corporation or any other governmental agency or instrumentality, nor are they obligations of, or guaranteed by, a bank.

You should read this document together with the related product supplement, index supplement, tax supplement and prospectus, each of which can be accessed via the hyperlinks below. Please also see “Additional Terms of the Securities” and “Additional Information About the Securities” at the end of this document.

References to “we,” “us” and “our” refer to Morgan Stanley or MSFL, or Morgan Stanley and MSFL collectively, as the context requires.

Product Supplement for Principal at Risk Securities dated April 8, 2026 Index Supplement dated April 8, 2026

Tax Supplement dated April 8, 2026 Prospectus dated April 8, 2026

 

Morgan Stanley Finance LLC

Dual Directional Buffered PLUS Principal at Risk Securities

 

 

Terms continued from the previous page
Payment at maturity per security:	•If the final level is greater than the initial level: (stated principal amount + leveraged upside payment), subject to the maximum upside payment at maturity •If the final level is equal to or less than the initial level but is greater than or equal to the buffer level: stated principal amount + (stated principal amount × absolute underlier return × absolute return participation rate) Under these circumstances, the payment at maturity will effectively be limited to a positive return of 10%. •If the final level is less than the buffer level: stated principal amount × (performance factor + buffer amount) Under these circumstances, the payment at maturity will be less, and may be significantly less, than the stated principal amount, subject to the minimum payment at maturity.
Final level:	The closing level of the underlier on the observation date
Initial level:	, which is the closing level of the underlier on the strike date
Leveraged upside payment:	stated principal amount × leverage factor × underlier percent change
Maximum upside payment at maturity:	$1,380 per security (138% of the stated principal amount)
Leverage factor:	200%
Underlier percent change:	(final level – initial level) / initial level
Buffer level:	, which is 90% of the initial level
Absolute underlier return:	The absolute value of the underlier percent change. For example, a -5.00% underlier percent change will result in a +5.00% absolute underlier return.
Absolute return participation rate:	100%
Performance factor:	final level / initial level
Buffer amount:	10%
Minimum payment at maturity:	10% of the stated principal amount
CUSIP:	61781FPZ0
ISIN:	US61781FPZ08
Listing:	The securities will not be listed on any securities exchange.

 

Morgan Stanley Finance LLC

Dual Directional Buffered PLUS Principal at Risk Securities

 

Estimated Value of the Securities

The original issue price of each security is $1,000. This price includes costs associated with issuing, selling, structuring and hedging the securities, which are borne by you, and, consequently, the estimated value of the securities on the pricing date will be less than $1,000. Our estimate of the value of the securities as determined on the pricing date will be within the range specified on the cover hereof and will be set forth on the cover of the final pricing supplement.

What goes into the estimated value on the pricing date?

In valuing the securities on the pricing date, we take into account that the securities comprise both a debt component and a performance-based component linked to the underlier. The estimated value of the securities is determined using our own pricing and valuation models, market inputs and assumptions relating to the underlier, instruments based on the underlier, volatility and other factors including current and expected interest rates, as well as an interest rate related to our secondary market credit spread, which is the implied interest rate at which our conventional fixed rate debt trades in the secondary market.

What determines the economic terms of the securities?

In determining the economic terms of the securities, we use an internal funding rate, which is likely to be lower than our secondary market credit spreads and therefore advantageous to us. If the issuing, selling, structuring and hedging costs borne by you were lower or if the internal funding rate were higher, one or more of the economic terms of the securities would be more favorable to you.

What is the relationship between the estimated value on the pricing date and the secondary market price of the securities?

The price at which MS & Co. purchases the securities in the secondary market, absent changes in market conditions, including those related to the underlier, may vary from, and be lower than, the estimated value on the pricing date, because the secondary market price takes into account our secondary market credit spread as well as the bid-offer spread that MS & Co. would charge in a secondary market transaction of this type and other factors. However, because the costs associated with issuing, selling, structuring and hedging the securities are not fully deducted upon issuance, to the extent that MS & Co. may buy or sell the securities in the secondary market during the amortization period specified herein, absent changes in market conditions, including those related to the underlier, and to our secondary market credit spreads, it would do so based on values higher than the estimated value. We expect that those higher values will also be reflected in your brokerage account statements.

MS & Co. may, but is not obligated to, make a market in the securities, and, if it once chooses to make a market, may cease doing so at any time.

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Morgan Stanley Finance LLC

Dual Directional Buffered PLUS Principal at Risk Securities

 

Hypothetical Examples

Hypothetical Payoff Diagram 

The payoff diagram below illustrates the payment at maturity for a range of hypothetical performances of the underlier over the term of the securities, based on the following terms:

Stated principal amount:	$1,000 per security
Leverage factor:	200%
Maximum upside payment at maturity:	$1,380 per security (138% of the stated principal amount)
Absolute return participation rate:	100%
Buffer level:	90% of the initial level
Buffer amount:	10%
Minimum payment at maturity:	10% of the stated principal amount
Hypothetical Payoff Diagram

￭Upside Scenario. If the final level is greater than the initial level, investors will receive the stated principal amount plus 200% of the appreciation of the underlier over the term of the securities, subject to the maximum upside payment at maturity.

oIf the underlier appreciates 5%, investors will receive $1,100 per security, or 110% of the stated principal amount.

oIf the underlier appreciates 100%, investors will receive only the maximum upside payment at maturity of $1,380 per security, or 138% of the stated principal amount.

￭Absolute Return Participation Scenario. If the final level is equal to or less than the initial level but is greater than or equal to the buffer level, investors will receive the stated principal amount plus a positive return equal to (i) the absolute value of the percentage decline in the level of the underlier multiplied by (ii) the absolute return participation rate. Under these circumstances, the payment at maturity will effectively be limited to a positive return of 10% per security.

oIf the underlier depreciates 5%, investors will receive $1,050 per security, or 105% of the stated principal amount.

￭Downside Scenario. If the final level is less than the buffer level, investors will receive an amount that is less, and may be significantly less, than the stated principal amount, based on a 1% loss of principal for each 1% decline in the level of the underlier beyond the buffer amount.

oIf the underlier depreciates 95%, investors will lose 85% of their principal and receive only $150 per security at maturity, or 15% of the stated principal amount.

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Morgan Stanley Finance LLC

Dual Directional Buffered PLUS Principal at Risk Securities

 

Risk Factors

This section describes the material risks relating to the securities. For further discussion of these and other risks, you should read the section entitled “Risk Factors” in the accompanying product supplement, tax supplement and prospectus. We also urge you to consult with your investment, legal, tax, accounting and other advisers in connection with your investment in the securities.

Risks Relating to an Investment in the Securities

￭The securities provide for only the minimum payment at maturity and do not pay interest. The terms of the securities differ from those of ordinary debt securities in that they provide for only the minimum payment at maturity and do not pay interest. If the final level is less than the buffer level, the payout at maturity will be an amount in cash that is less than the stated principal amount of each security, and you will lose an amount proportionate to the full decline in the level of the underlier over the term of the securities beyond the buffer amount. You could lose a significant portion of your initial investment in the securities.

￭The appreciation potential of the securities is limited by the maximum upside payment at maturity. Where the final level is greater than the initial level, the appreciation potential of the securities is limited by the maximum upside payment at maturity. Although the leverage factor provides enhanced exposure to any increase in the final level over the initial level, if the underlier appreciates over the term of the securities, under no circumstances will the payment at maturity exceed the maximum upside payment at maturity.

￭Any positive return on the securities that is based on the depreciation of the underlier is effectively capped. Any positive return on the securities that is based on the depreciation of the underlier will be capped, because the absolute return participation feature is operative only if the level of the underlier has not declined below the buffer level on the observation date. Any decline in the level of the underlier beyond the buffer level will result in a loss, rather than a positive return, on your initial investment in the securities.

￭The amount payable on the securities is not linked to the value of the underlier at any time other than the observation date. The final level will be based on the closing level of the underlier on the observation date, subject to postponement for non-trading days and certain market disruption events. Even if the value of the underlier appreciates prior to the observation date but then drops by the observation date, the payment at maturity may be less, and may be significantly less, than it would have been had the payment at maturity been linked to the value of the underlier prior to such drop. Although the actual value of the underlier on the stated maturity date or at other times during the term of the securities may be higher than the closing level of the underlier on the observation date, the payment at maturity will be based solely on the closing level of the underlier on the observation date.

￭The market price of the securities may be influenced by many unpredictable factors. Several factors, many of which are beyond our control, will influence the value of the securities in the secondary market and the price at which MS & Co. may be willing to purchase or sell the securities in the secondary market. We expect that generally the value of the underlier at any time will affect the value of the securities more than any other single factor. Other factors that may influence the value of the securities include:

othe volatility (frequency and magnitude of changes in value) of the underlier;

ointerest and yield rates in the market;

ogeopolitical conditions and economic, financial, political, regulatory or judicial events that affect the underlier or markets generally;

othe availability of comparable instruments;

othe composition of the underlier and changes in such composition;

othe time remaining until the securities mature; and

oany actual or anticipated changes in our credit ratings or credit spreads.

Some or all of these factors will influence the price that you will receive if you sell your securities prior to maturity. Generally, the longer the time remaining to maturity, the more the market price of the securities will be affected by the other factors described above. For example, you may have to sell your securities at a substantial discount from the stated principal amount if, at the time of sale, the closing level of the underlier is at, below or not sufficiently above the buffer level, or if market interest rates rise.

You can review the historical closing levels of the underlier in the section of this document called “Historical Information.” You cannot predict the future performance of the underlier based on its historical performance. The value of the underlier may be, and has recently been, volatile, and we can give you no assurance that the volatility will lessen. There can be no assurance that the final level will be greater than or equal to the buffer level so that you do not suffer a loss on your initial investment in the securities.

￭The securities are subject to our credit risk, and any actual or anticipated changes to our credit ratings or credit spreads may adversely affect the market value of the securities. You are dependent on our ability to pay all amounts due on the securities, and, therefore, you are subject to our credit risk. The securities are not guaranteed by any other entity. If we default on our obligations under the securities, your investment would be at risk and you could lose some or all of your investment. As a result, the market value of the securities prior to maturity will be affected by changes in the market’s view of our creditworthiness.

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Morgan Stanley Finance LLC

Dual Directional Buffered PLUS Principal at Risk Securities

 

Any actual or anticipated decline in our credit ratings or increase in the credit spreads charged by the market for taking our credit risk is likely to adversely affect the market value of the securities.

￭As a finance subsidiary, MSFL has no independent operations and will have no independent assets. As a finance subsidiary, MSFL has no independent operations beyond the issuance and administration of its securities and will have no independent assets available for distributions to holders of MSFL securities if they make claims in respect of such securities in a bankruptcy, resolution or similar proceeding. Accordingly, any recoveries by such holders will be limited to those available under the related guarantee by Morgan Stanley and that guarantee will rank pari passu with all other unsecured, unsubordinated obligations of Morgan Stanley. Holders will have recourse only to a single claim against Morgan Stanley and its assets under the guarantee. Holders of securities issued by MSFL should accordingly assume that in any such proceedings they would not have any priority over and should be treated pari passu with the claims of other unsecured, unsubordinated creditors of Morgan Stanley, including holders of Morgan Stanley-issued securities.

￭The rate we are willing to pay for securities of this type, maturity and issuance size is likely to be lower than the rate implied by our secondary market credit spreads and advantageous to us. Both the lower rate and the inclusion of costs associated with issuing, selling, structuring and hedging the securities in the original issue price reduce the economic terms of the securities, cause the estimated value of the securities to be less than the original issue price and will adversely affect secondary market prices. Assuming no change in market conditions or any other relevant factors, the prices, if any, at which dealers, including MS & Co., may be willing to purchase the securities in secondary market transactions will likely be significantly lower than the original issue price, because secondary market prices will exclude the issuing, selling, structuring and hedging-related costs that are included in the original issue price and borne by you and because the secondary market prices will reflect our secondary market credit spreads and the bid-offer spread that any dealer would charge in a secondary market transaction of this type as well as other factors.

The inclusion of the costs of issuing, selling, structuring and hedging the securities in the original issue price and the lower rate we are willing to pay as issuer make the economic terms of the securities less favorable to you than they otherwise would be.

However, because the costs associated with issuing, selling, structuring and hedging the securities are not fully deducted upon issuance, to the extent that MS & Co. may buy or sell the securities in the secondary market during the amortization period specified herein, absent changes in market conditions, including those related to the underlier, and to our secondary market credit spreads, it would do so based on values higher than the estimated value, and we expect that those higher values will also be reflected in your brokerage account statements.

￭The estimated value of the securities is determined by reference to our pricing and valuation models, which may differ from those of other dealers and is not a maximum or minimum secondary market price. These pricing and valuation models are proprietary and rely in part on subjective views of certain market inputs and certain assumptions about future events, which may prove to be incorrect. As a result, because there is no market-standard way to value these types of securities, our models may yield a higher estimated value of the securities than those generated by others, including other dealers in the market, if they attempted to value the securities. In addition, the estimated value on the pricing date does not represent a minimum or maximum price at which dealers, including MS & Co., would be willing to purchase your securities in the secondary market (if any exists) at any time. The value of your securities at any time after the date of this document will vary based on many factors that cannot be predicted with accuracy, including our creditworthiness and changes in market conditions. See also “The market price of the securities may be influenced by many unpredictable factors” above.

￭The securities will not be listed on any securities exchange and secondary trading may be limited. The securities will not be listed on any securities exchange. Therefore, there may be little or no secondary market for the securities. MS & Co. may, but is not obligated to, make a market in the securities and, if it once chooses to make a market, may cease doing so at any time. When it does make a market, it will generally do so for transactions of routine secondary market size at prices based on its estimate of the current value of the securities, taking into account its bid/offer spread, our credit spreads, market volatility, the notional size of the proposed sale, the cost of unwinding any related hedging positions, the time remaining to maturity and the likelihood that it will be able to resell the securities. Even if there is a secondary market, it may not provide enough liquidity to allow you to trade or sell the securities easily. Since other broker-dealers may not participate significantly in the secondary market for the securities, the price at which you may be able to trade your securities is likely to depend on the price, if any, at which MS & Co. is willing to transact. If, at any time, MS & Co. were to cease making a market in the securities, it is likely that there would be no secondary market for the securities. Accordingly, you should be willing to hold your securities to maturity.

￭As discussed in more detail in the accompanying product supplement, investing in the securities is not equivalent to investing in the underlier(s).

￭The U.S. federal income tax consequences of an investment in the securities offered by this pricing supplement are uncertain. There is no direct legal authority regarding the proper U.S. federal income tax treatment of the securities, and significant aspects of the tax treatment of the securities are uncertain. You should review carefully the section entitled “United States Federal Income Tax Considerations” herein, in combination with the section entitled “United States Federal Taxation” in the accompanying tax supplement, and consult your tax adviser regarding the U.S. federal income tax consequences of an investment in the securities.

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Morgan Stanley Finance LLC

Dual Directional Buffered PLUS Principal at Risk Securities

 

Risks Relating to the Underlier(s)

￭Because your return on the securities will depend upon the performance of the underlier(s), in addition to any risks described further below, the securities are subject to the following risk(s) discussed in more detail in the accompanying product supplement.

oAdjustments to an underlying index could adversely affect the value of the securities.

Risks Relating to Conflicts of Interest

In engaging in certain activities described below and as discussed in more detail in the accompanying product supplement, our affiliates may take actions that may adversely affect the value of and your return on the securities, and in so doing they will have no obligation to consider your interests as an investor in the securities.

￭The calculation agent, which is a subsidiary of Morgan Stanley and an affiliate of MSFL, will make determinations with respect to the securities. As calculation agent, MS & Co. will make any determinations necessary to calculate any payment(s) on the securities. Moreover, certain determinations made by MS & Co., in its capacity as calculation agent, may require it to exercise discretion and make subjective judgments, which may adversely affect your return on the securities. In addition, MS & Co. has determined the estimated value of the securities on the pricing date.

￭Hedging and trading activity by our affiliates could potentially adversely affect the value of the securities.

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Morgan Stanley Finance LLC

Dual Directional Buffered PLUS Principal at Risk Securities

 

Historical Information

S&P 500® Index Overview

Bloomberg Ticker Symbol: SPX

The S&P 500® Index is intended to provide a benchmark for performance measurement of the large capitalization segment of the U.S. equity markets by tracking the stock price movement of 500 companies with large market capitalizations. The underlying index publisher with respect to the S&P 500® Index is S&P® Dow Jones Indices LLC, or any successor thereof. Component stocks of the S&P 500® Index are required to have a total company level market capitalization that reflects approximately the 85th percentile of the S&P® Total Market Index. The S&P 500® Index measures the relative performance of the common stocks of 500 companies as of a particular time as compared to the performance of the common stocks of 500 similar companies during the base period of the years 1941 through 1943. For additional information about the S&P 500® Index, see the information set forth under “S&P® U.S. Indices—S&P 500® Index” in the accompanying index supplement.

The closing level of the underlier on April 29, 2026 was 7,135.95. The following graph sets forth the daily closing levels of the underlier for the period noted below. We obtained the historical information presented in this document from Bloomberg Financial Markets, without independent verification. The underlier has at times experienced periods of high volatility. You should not take the historical closing levels of the underlier as an indication of its future performance, and no assurance can be given as to the closing level of the underlier at any time.

 

Underlier Daily Closing Levels January 1, 2021 to April 29, 2026

 

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Morgan Stanley Finance LLC

Dual Directional Buffered PLUS Principal at Risk Securities

 

Additional Terms of the Securities

Please read this information in conjunction with the terms on the cover of this document.

Additional Terms:
If the terms described herein are inconsistent with those described in the accompanying product supplement, index supplement, tax supplement or prospectus, the terms described herein shall control.
Denominations:	$1,000 per security and integral multiples thereof
Dual Directional Buffered PLUS:	The accompanying product supplement refers to these Dual Directional Buffered PLUS as the “securities.”
Amortization period:	The 6-month period following the issue date
Trustee:	The Bank of New York Mellon
Calculation agent:	Morgan Stanley & Co. LLC (“MS & Co.”)

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Morgan Stanley Finance LLC

Dual Directional Buffered PLUS Principal at Risk Securities

 

Additional Information About the Securities

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Morgan Stanley Finance LLC

Dual Directional Buffered PLUS Principal at Risk Securities

 

 

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