If I load a full novel (170k words, no comments or footnotes) in scrivenings mode, it uses about 2GB of ram. But after leaving it for a while (not sure how long, at least a day it seems) it will drop down to about 170MB and stay there even if I scroll through the novel and edit different sections.
Memory on the computer is there to be used by all the apps and processes running, managed by those apps and processes.
Are you having a problem doing your writing with Scrivener?