little to no lag is the goal.
The game is around 40K+ Parts and growing.
We tried reducing non-essential parts and increasing the unions with existing parts.
The game just cannot handle well at all for those without really good PC’s or such and this is a large issue as it needs to be mobile and Lower End PC compatible.
I spoke extensively about making large maps while being performance friendly in my RDC talk:
And depending on how you’re using Unions, they could actually be doing a lot more harm than good. 40k Parts isn’t usually a lot depending on how they’re used, but we’d need to see the memory use breakdown to be sure.
As @Aotrou said it can depend on how you use unions I also know excessive unions can cause lag. That’s why I recommend using blender meshes when building large builds I’ve found it to decrease lag when you use low poly meshes.
Theres also a considerably large amount of terrain I should mention sorry.
Can you share the Memory Usage of the game, as well as plenty of pictures so we can actually help you 
Scroll down on that screen to show Place Memory (I say this in my RDC talk).
However off the bat, 2000 mb is a lot of memory use. So already I can see you have a big problem.
Im just getting that data for you, However this is the issue indeed, As we have not even inserted the
citys and such yet.
You’re using a lot of textures. 934 mb worth - about 40% of that 2200 mb. Cut that down, remove Unions in favor of MeshParts or basic Parts, and also simplify the Terrain where you can, the 410 mb there is no joke either.
Thank you, Your amazing as always.
