Reduce mem use so I can switch out of PS

Recently I switched to PS. What a mistake that was!

It turns out that my sites, which don’t attract all that much traffic, uses 500m->1gb of memory. What the heck?

When I reboot the server, memory utilization zooms immediately to 580mb of memory. I can only realistically afford the most basic PS settings of 150mb.

How can I reduce the ram consumption of my accounts? All I really have running is wordpress.

How can I even figure out who is consuming all the ram?