Map lag on only one map?

My brother lags alot on the map rp_industrial17_v1 but not on any other map, and he has a better computer than me but I dont lag on that map.
Does anyone know why? ITZ STRANGGGGGGGGE

There could be a large number of contributing factors. These could include the applications running in the background of the computer, the quality of the computer, what addons you are running with gmod, the quality of the map, etc etc etc.

Double check that your brother is not running several instances of youtube or streaming gay porn in the background, do a scan for malware using MalwareBytes or any other anti-malware software, and clean out any unneeded addons.

Any console errors? The lag can happen from a missing texture/model that has no fallback.

Yea that was the problem, he had 21 gay porn sites up and was watching pewdiepie…