If you're running luna classic server, 16gb of ram is fine if you want to run all maps. If luna plus, I think 20gb of ram if you want to run all luna plus maps. If you're just testing and don't want to upgrade your ram, why not close the maps that you don't plan to go to atm? Just run the maps that you want to use and close other maps. That wont make your map servers crash. If they crash with only a few maps running, then there might've been an error that occurred in the map server. Check the logs