If My Game Starts slow if i add Mesh Collider to my whole environment, Should i do something else?

I made my environment by using “Walled City” from daz.

I actualy made 3 copies of it and connected it.

Well when i did that and press playe to test it out, it lagged, it didn’t necesariliy lag the game but before the game started, it lagged the system for a bit.

I 've also heard that Mesh colliders slow things down, so it’s not good to use as i used it?

From what I know mesh colliders are pretty costly so putting one on a whole city would be very inefficient. I’d say that is likely the cause of your lag. The alternatives take longer but are a lot better.

You can either make a bunch empty objects with a box/sphere/etc colliders on them and place them where needed, or make another far simpler model and use a mesh collider on that. This would look like the city but it wouldn’t have all the details and stuff on it, just simple walls and what not. It wouldn’t have anything at places where the collisions aren’t needed but detail is (such as stuff on a roof you can’t get to).