Sorry to hear that. The map requires more system resources than most other GMod maps. When combined with other resource-hungry addons, it might become too much for the game or your system to handle once you enter the bunker. Try disabling other addons and restarting the game before playing.

Switching to the 64-bit branch of GMod might also help, but keep in mind that this is still a beta. To do this, right-click GMod in your Steam library and click Properties. Next, go to the Betas tab and opt into the beta branch titled x86-64.