Very laggy with npcs

When I have alot of Npcs, or loads of props, things get very very laggy… what can i do to stop this happening? stuff like defrag, change graphics settings… any general tips would be helpfull
Im posting on behalf of a friend so i will post his specs when i go round in a little while…

Well, I guess if you want to speed things up a little you could update your graphics card. That has worked for me in the past. also I find that some times it helps to run a game booster. And there are clever people who know what to change the launch options to that make things run faster but I’m not one of those people sadly.

Thanks for the help.
Whats a game booster?