For most people (average PC user), 16GB is more than enough. Your 65% usage is getting close to where you may need to consider upgrading (usually around 70-80% consistent usage). You may also want to run Task Manager and see if there's a lot of crap running that use up memory. Unless you're running VM's, doing a lot of content creation, etc., you may not need more, but it all depends on what you do and use. For a gaming PC, 16GB should probably be the minimum. I have 32GB, and even when I'm playing games, playing around with programming, etc. I rarely go over 16-18 GB from what I recall with dev IDE's, databases, spreadsheets, games, browsers, etc. all open at the same time. I don't ever recall getting close to 32 GB even when running a VM. I may have hit 20-22GB usage (?) a few times. I'll be looking to build a new PC here in the next 6 or so months, probably, and I'll either get 32 GB of RAM or, if it's cheap enough (which it probably won't be), get 64 GB for giggles.
