I have an old 915 sitting right next to an 016 in my garage - the 915 is fatter, shorter, heavier and has a much different bell housing configuration.
Personally, I know everyone wants the G50XXX (if they're going with a porsche transaxle) but a 915 is going to be a stronger box than an 016 by quite a bit I think. It has the same bell housing design as the G50.