(OOF. This is the 7th time that I answer a topic like this, hmmm…)
By the way, below there are some solutions that you can apply to your game:
- Remove the terrain that you don’t see
- Enable streaming (for more informations Content streaming )
- Disable Cast Shadows in the parts that doesn’t need shadows
- Optimize your scripts
- Use meshes (how to create a mesh from a building you did in studio meshes )
- Optimise the collions box (for other building tips here )
- Remove Can Collide to parts that you can’t touch
You can have some viruses some make sure that any script hasn’t a require() function unless you know what it requires; search for backdoors too! (Most common backdoors uses require() )
It can be a plugin too!
(Another thing you can do is to open the Game Explorer tab, and delete images, assets… that you don’t use)
Good luck from Italy (ciao) 
PS: Sorry for the bad English