Whenever you move assets from one project to another the objects always inherit the current settings of your project you are in.
IE
1.) Lod’s
2.) Static/Movable/Stationary LIghting
3.) Post Processing effects
4.) Depth of field
5.) Level Streaming
etc.
Basically if you move any asset from one project to another then you will need to reoptimize. Even after optimization you will still need to be discreet about the amount you use.
For instance if you have 1,000 instances of a 3,000 polygon mesh, well that usually boosts your render time due to the calculations your computer will need to make.
Hope this helps you out.