This is a bit questionable since I have 0 idea how this games codes work (and being a dogshit coder myself) BUT
Is it possible to have the ground lights light up in different times rather than all lighting up when it turns to night time ?
Like for example part of the maps lets say 1/4 of them lights up, then the next 1/4, etc etc
I dont know how much it might change the peformance but atleast this should help reduce some lag spikes since not all lights are lighting up and the exact same time, just slowly let it render one by one.