Form of Non-Statutory Stock Option Agreement (Non-Employee Directors) under the Foghorn Therapeutics Inc. 2020 Equity Incentive Plan

Exhibit 10.15

FOGHORN THERAPEUTICS INC.

2020 EQUITY INCENTIVE PLAN

NON-STATUTORY STOCK OPTION AGREEMENT

(NON-EMPLOYEE DIRECTORS)

This agreement (this “Agreement”) evidences a stock option granted by Foghorn Therapeutics Inc. (the “Company”) to the individual named above (the “Participant”), pursuant to and subject to the terms of the Foghorn Therapeutics Inc. 2020 Equity Incentive Plan (as from time to time amended and in effect, the “Plan”). Except as otherwise defined herein, all capitalized terms used herein have the same meaning as in the Plan.

1. Grant of the Stock Option. The Company grants to the Participant on the date set forth above (the “Date of Grant”) an option (the “Stock Option”) to purchase, pursuant to and subject to the terms set forth in this Agreement and in the Plan, up to the number of shares of Stock set forth above (the “Shares”) with an exercise price per Share as set forth above, in each case, subject to adjustment pursuant to Section 7 of the Plan in respect of transactions occurring after the date hereof.

The Stock Option evidenced by this Agreement is a non-statutory option (that is, an option that is not intended to qualify as an ISO) and is granted to the Participant in connection with the Participant’s Employment.

2. Vesting. The term “vest” as used herein with respect to the Stock Option or any portion thereof means to become exercisable, and the term “vested” with respect to the Stock Option or any portion thereof means that the Stock Option (or portion thereof) is then exercisable. Unless earlier terminated, forfeited, relinquished or expired, the Stock Option will vest [as to one-third of the Shares underlying the Stock Option on each of the first three anniversaries of the Date of Grant (with the number of Shares that vest on any date being rounded down to the nearest whole Share and the option becoming vested as to 100% of the Shares on the third anniversary of the Date of Grant)]1[in full on the first anniversary of the Date of Grant]2, subject to the Participant’s continued Employment through [each][the] applicable vesting date.

3. Exercise of the Stock Option. No portion of the Stock Option may be exercised until such portion vests. Each election to exercise any vested portion of the Stock Option will be subject to the terms and conditions of the Plan and must be in written or electronic form acceptable to the Administrator, signed (including by electronic signature) by the Participant or, if at the relevant time the Stock Option has passed to the estate or beneficiary of the Participant or to a

permitted transferee, such estate or beneficiary or permitted transferee. Each such written or electronic exercise election must be received by the Company at its principal office or by such other party as the Administrator may prescribe and must be accompanied by payment in full of the exercise price by cash or check, through a broker-assisted exercise program acceptable to the Administrator, or as otherwise provided in the Plan. The latest date on which the Stock Option or any portion thereof may be exercised is the tenth (10th) anniversary of the Date of Grant and, if not exercised by such date, the Stock Option or any remaining portion thereof will thereupon immediately terminate.

4. Cessation of Employment. If the Participant’s Employment ceases, the Stock Option, to the extent not then vested, will be forfeited immediately for no consideration, and any vested portion of the Stock Option that is then outstanding will remain exercisable for the period described in Section 6(a)(4) of the Plan.

5. Restrictions on Transfer. The Stock Option may not be transferred except as expressly permitted under Section 6(a)(3) of the Plan.

6. Forfeiture; Recovery of Compensation. By accepting, or being deemed to have accepted, the Stock Option, the Participant expressly acknowledges and agrees that his or her rights, and those of any permitted transferee, with respect to the Stock Option, including the right to any Shares acquired under the Stock Option or proceeds from the disposition thereof, are subject to Section 6(a)(5) of the Plan (including any successor provision). The Participant further agrees to be bound by the terms of any clawback or recoupment policy of the Company that applies to incentive compensation that includes Awards such as the Stock Option. Nothing in the preceding sentence will be construed as limiting the general application of Section 8 of this Agreement.

7. Taxes. The Participant is responsible for satisfying and paying all taxes arising from or due in connection with the Stock Option, its exercise or a disposition of any Shares acquired upon exercise of the Stock Option. The Company will have no liability or obligation related to the foregoing.

8. Provisions of the Plan. This Agreement is subject in its entirety to the provisions of the Plan, which are incorporated herein by reference. A copy of the Plan as in effect on the Date of Grant has been made available to the Participant. By accepting, or being deemed to have accepted, the Stock Option, the Participant agrees to be bound by the terms of the Plan and this Agreement. In the event of any conflict between the terms of this Agreement and the Plan, the terms of the Plan will control.

9. Acknowledgements. This Agreement represents the entire agreement and understanding between the parties hereto with respect to the subject matter hereof, and supersedes all prior and contemporaneous communications, agreements and understandings, written or oral, relating thereto. This Agreement may be executed in counterparts (and may be delivered by email or other electronic means), each of which will be deemed an original and all of which together will constitute one and the same instrument.

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IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of the date first written above.

[Signature Page to Stock Option Agreement]