The size of you building pieces will contribute in the memory of the game. An empty build with 10000 pieces will render faster on ps4 than a small build filled with decorations and animations.
What troubles me is not how lags are created from our builds.
Neither from decorations or chests filled with materials and light or thrall animations. Because for a player who plays in old consoles this can be adjusted easily.
The fact that the knowledge you gain creates lags was my last “invent” and it really bothered me a lot 
.
I understood this when i did this play through…
On exile lands i took zero knowledge, i build zero items except some campfires and bedrolls here and then, so the whole play through went with stunning performance.
In Siptah however inside the vaults i find recipes and i was consuming them. After each use of recipe consumption i had lags. I had ro quit game and load back in to be released from them . THIS is not good because you need the recipes and it’s something no player should have limitation!