There have been a few threads on mil-dots that have stated that Bushnell are "true" at 15x where pretty much every other scope is "true" at 10x ( or Hawkes 20x ret) personally I don't know.

All it means in practical terms is Chairgun type dot range zero's (holdover) will be out because their maths is at 10x true. but their 10x holdover will be your 15x their 5x your 7.5x their 6.6x your 10x, their 3.3x your 5x etc (if you follow)