I remember when in Creative 2.0 a few updates ago, things started to cost less memory which took my map from 109,000 to about 60,000 so I added more to it.
Later on the memory usage jumped up again, but I could return to lobby, go back in my map and it would be right.
Maybe three updates ago memory usage is now over 115k and nothing I do short of deleting things will bring it down.