Uses of RAM depends upon the applications running on your sysytem, OS nothing got much to do with it. Now if you ask about internal processes that runs by OS, you got manually to stop them. Like in Windows 10 there are lots of applications that begin running when you start your system, these apps occupy RAM unnecessarily. So go to task manger disable those apps.
Windows 10 is much more optimized than previous versions, “6gb- busting ass to perform task” , it sounds like lots of background processes are running unnecessarily.
First check for those unwanted piece of third party software those gets installed while installing some other software.
Second Clean your temporary files, unwanted and useless files, for that use Disk Cleanup, it’s comes pre-installed in Windows.
Third use Disk defragmentation and Optimization for optimizing disk-space allocation, this also comes pre-installed in Windows .
If problem still persist it’s time to re-install your OS while in Windows 10 REFRESHoption is there try that one.
And coming to your questions you don’t need to take all these headache of maintaining your system if you are using any Linux distro. So yes Linux/Ubuntu in that case uses less RAM compare to Windows 10.