Gnome-Software is running in the background consuming 200-500mb RAM. If updates are automated or primarily via apt-get, this can be disabled. It autostarts during boot and is hidden from the autostart menu.
vi ~/.config/autostart/gnome-software-service.desktop # or sudo vi /etc/xdg/autostart/gnome-software-service.desktop
change NoDisplay=true to false.
Then open Startup Applications via the start menu and disable the Gnome Software entry.