Maybe total count is lower than Caucasus, but unique items are probably significantly higher. Whereas you can copy/paste objects that have already been rendered in Caucasus map, you have to render each unique item in PG map.
And I only have 16gig of RAM as well. I can play PG single player fine, but if I go to Multiplayer and am anywhere near a city...I might as well play another game, since I crash back to desktop every time (after hitting 0 FPS for like 5min).