Join a empty multiplayer server and check that your FPS is limited by the server(low CPU/GPU usage) raising draw distance can help with this.

Kavala is a good place to test as you can follow the main road going N/S through the town and there are quite a few active lights along the way/side roads that you can fire at.

Pick a spot near town that you set a waypoint to for getting a "before and after" point, screenshot or just remember what kind of FPS you are getting when standing there.

Walk/drive along the road and disable any and all lights you come across at least untill you get to the center of town before going back to your waypoint and compare FPS with what you had before, should be slightly higher wich means for some reason the server is now able to run sliiiightly faster than before.

This has only been tested on empty KotH servers and I have only done it 3 times but all 3 times there has been an increase in FPS and this includes when its day and the street lights are "off".

I have no experience with any map editor for Arma 3, otherwise I would try to remove ALL street lights from the entire map to easier be able to compare performance with/without them as the increase I have seen is fairly small and usually just 1-2 FPS, its not impossible its just a big coincidence but since so far its a 100% deal and the street lights I have disabled are few in number to get that increase, Im reporting this here on the off chance that the street lights are for some reason a drain on the servers(and what if all street lights all over Altis were having this effect?).