Is this a seed generated through the game or through GTXGaming? I am with LogicServers for my host, and my server is hosting a seed that I generated through the game (not any of the preinstalled maps). If you go through the 7DTD client and not through the GTX gaming, it uses much less RAM and CPU compared to doing it through the server. It takes 3x longer to generate the map but in the end we can get by on a 6k custom seed map with 10 players and use less than our 6GB RAM limit.
Good example from testing so far, is 10K RWG on our server takes around 14GB RAM to create. On a client if you create it then upload the folders to the server and set your configs to the same values for GameName, WorldType, Size, Seed to load up the same RWG that you created and uploaded, it'll use around 6-7GB.