I just bought and installed v16 Pro Suite, and it took the latest Boris key and Sapphire 11 lights included in the suite (which is OK) but if you have Boris element 3d objects and sapphire Render unit from the Vegas 15 suite, you loose those on both the 15 and 16 installs (BCC replaces them with the upgraded version of which your license from 15 suite is not valid anymore).
It is a bit like the Mercalli stabilizer story when going from Vegas 14 to 15, but that was worse, as the Mercalli was the same version. Here at least you get an updated version with mocha... Still that was a disappointment, Boris should not wipe the older versions if you are happy with it.
On the bright side I immediately see the effect of the new high DPI setting for monitors (off by default, so you need to enable it). Text is much sharper on a high DPI monitor.