The majority of your payload will not come from the operating system, or desktop but from the applications. Web browsers and sites are heavy these days and Chrome or Firefox will easily consume more RAM than your operating system and desktop altogether.

In the shot below we have Chrome running with 3 tabs, LibreOffice Writer with an empty document and GIMP without any image file opened. Combined they are already taking about 400 megs and the number will grow a lot once you get going with your work, whatever it is. So if you want to save some RAM, you need to choose lighter weight applications, but they are rarely full-featured.