I have no idea how to stop the lag. I mean you could lower your graphics quailty or add a hide stuff far away from you script. But anyways, really good job!
Turn on streamingEnabled and adjust distance, also turn off collisions on anything that doesnt require it.
If it stutters on every load there might be alot of stuff unanchored that you didn’t realise which could cause fps drops briefly, other than than you could lower the amount of spotlights or sub them out for pointlights/surfacelights while using pointlights to light up massive areas.
Your trees if imported from blender/the toolbox could have really bad collisionfidelity so be sure to set them to Box/Hull depending on how accurate you want hitboxes to be.
I really like the builds though, good job! making this map in under 2 months is very impressive