Memory/CPU usage comparison between two MacBook Pros
It is rather difficult to compare a fresh 'cold' new system with a 'warm' fully synchronized and updated one.  New Macs have a lot of catching up to do; iCloud service syncing and system patches being two of them.

On the other hand OSX - and every other OS really - chooses a healthy part of the available RAM (real, physical memory) above swapping to disk (virtual memory) for obvious reasons.  Having 8 more Gigs available probably decreased your swap file by a couple gigs.  Granted, swapping to those post-2013 SSD's is reasonably fast, but no (or less) swapping is always faster (and better for your battery).

Chances are high your increased RAM usage is part of those 2 reasons.