Depending on the rates and down payment, it's not uncommon to need >10% gains in the invested difference for the 30-year to beat the 15-year mortgage. The 15-year mortgage has proved to be much more advantageous in my case.
For sure. In another post I compared today's rates for 30Y and 15Y with 15 years of 4% returns and still came out (slightly) ahead. I'm interested in how you determined that the 15 year was more advantageous (did you calculate what your cash flow would have been with a 30Y?) and if it was a big advantage because you perhaps got lucky with market timing and finishing up your mortgage when the market is low (which really isn't something a new mortgager can rely on), or because the interest rates were at parity with the investment returns of that era, which would make it smarter to pay off quickly.
See https://www.mtgprofessor.com/A%20-%20Term/30_years_or_15.htm