I think you already have but if you didn't please check and do these -
-Make sure your graphics drivers are fully updated
-Verify the integrity of your game files at
http://pandahut.net/validate
-Completely uninstall then reinstall Unturned
-Worst case scenario, try doing a full wipe on your computer and reinstalling Windows
And again, like Mushy said - You could try downloading
Razer Cortex (it's safe, don't worry) to see if you're able to play for a longer period of time. Also check to see if all the fans on your computer are working properly, including your video card fans, as it could be an overheating issue.
Please look over all these things. If well none of them fix it, it may be your PC or Unturned itself. Personally I have no problems with these maps.