Key question to ask...why stop at 15? Why not 21 or 37? I will admit...somewhere down the line over the past hundred years...some text should have been added to the Supreme Court to indicate a number of some type.
I think a lot of people now (both sides of the aisle) would agree to a retirement age stipulation for the judges.
Brazil has 11, Costa Rica has 22, El Salvador has 15.
We would essentially and officially become a BANANA REPUBLIC................................
https://www.nationmaster.com/country-info/stats/Government/Judicial-branch