I am finding if I don’t have the old 15 object loaded when I save back as a 15 file then there is no conversion and the library report just it as a missing version 16 object.
But it is late now so I will test it out more thoroughly tomorrow.
Versions 6.5 to 22
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision M6800 - i7 4700MQ @ 2.40GHz, 16GB RAM, AMD FirePro M6100 (2GB), Windows 7 64bit