yes the business interest goes on line 15
look at line 22 of page 1 of the 1065 and then look at the total of net income reported on the k-1's lines 1. 2 or 3. they should be the same
the line 20 amount has a special purpose - in computing any limitation on losses due to lack of tax basis.
Line 20 Code N. Business interest expense. For tax years beginning after November 12, 2020, the partnership will report your share of the partnership's deductible business interest expense for inclusion in the separate loss class for computing any basis limitation (defined in section 704(d), Regulations section 1.163(j)-6(h)). This information is necessary if your losses are limited under section 704(d). Deductible business interest expense is reported elsewhere on Schedule K-1 and the total amount is reported here for information only and was
already included as a deduction on another line of your Schedule K-1. Included in the code N information is a statement providing the allocation of the business interest expense already deducted by the partnership by line number on the Schedule K-1. The partner must remove the business interest expense deductions from these referenced lines when computing any basis limitation. Any excess business interest expense not deductible under section 163(j) will be included in box 13, code K, for inclusion in the basis limitation and is not reported here. See Worksheet for Adjusting the Basis of a Partner's Interest in the Partnership for additional information about computing the loss limitation.
