Question: I want to borrow ₹25,00,000 at 8.5% per annum reducing balance. Comparing a 15-year tenure against a 20-year tenure (both monthly EMI), roughly how much MORE total interest will I end up paying if I choose the 20-year option instead of the 15-year option?
Answer: Approximately ₹7,75,611 more in total interest over the loan's life with the 20-year tenure, even though the 20-year EMI (≈₹21,696) is lower than the 15-year EMI (≈₹24,618).

Supporting evidence:
title: Inline formula / method note
quote: Standard loan amortization (EMI and total interest) formulas, compared across tenures
context: Standard loan amortization (EMI and total interest) formulas, compared across tenures.