You start off with telling us to not shutdown player server, then you complain about lag? I mean, it's pretty straight forward. The more servers that are up = more lag on the servers. Also if you'd like more RAM on your server just get more player slots.
Here you mentioned your server shutting down at random moment. Before I get to that, I'll just let you know, servers with no players do get shutdown after 5 minutes with no activity.
If your server shut down at a random moment, that's most likely because you edited a file wrong, check your logs and look for keywords such as "[ERROR]". I've never heard of a server with several players being shutdown for no reason and no traceable information in the logs.