1. Try unistalling all the addons to the server then reinstall all of them, then try.
2. Open Task Manager by searching it up in the search bar at the bottom left, once you have G-Mod opened go to "Details" in the task manager, find HL2-EXE then right click it > Set priority > High | This could improve load speed.
3. Close all other programs like discord, TS, ect ( Excluding Steam since you need it opened to even open up G-Mod ) | Personally this upped by load-in speed a lot.
These are all things that have worked for me, and I have a pretty bad PC so it should work for you. If you are still having problems, make a ticket in the main discord about this issue.