Snap-store is always running
The high memory consumption is a known issue. You can let the developers know it affects you by logging in and clicking on This bug affects XXX people. Does this bug affect you? at the top. It's not a good idea to add a comment there just for this purpose, even after many people already did it.
If, like me, you don't need it, you can uninstall it as recommended here (note you don't need gnome-software if you plan to only install snaps from the command line):
sudo snap remove snap-store