From the Partner's Instructions for Schedule K-1 box 13:
Code R. Pensions and IRAs. Payments made on your behalf to an IRA, qualified plan, simplified employee pension (SEP), or a SIMPLE IRA plan. See the Schedule 1 (Form 1040) instructions for line 19 to figure your IRA deduction. Enter payments made to a qualified plan, SEP, or SIMPLE IRA plan on line 15 of Schedule 1 (Form 1040). If the payments to a qualified plan were to a defined benefit plan, the partnership should give you a statement showing the amount of the benefit accrued for the current tax year.
Find additional information at the following link:
IRS Partner's Instructions for Schedule K-1
Line 15 of Schedule 1 for Form 1040 is referring to the Self-Employed Retirement Plan Contributions Line
(15 Self-employed SEP, SIMPLE, and qualified plans).
Line 15 Self-Employed SEP, SIMPLE, and Qualified Plans If you were self-employed or a partner, you may be able to take this deduction. See Pub. 560
