How many windows do you have open? 10 GB of RAM is a very large amount for WindowServer to use.
To answer your question, I have a total of 73 windows open at the moment. 11 of them are from applications with a single window open, 8 are from iTerm, and 54 are from Sublime Text. I am aware that is quite a lot for Sublime, but that is just how I use it.
Regardless, I just quit Sublime Text, and the memory usage only dropped to 8.9GB still absurdly high for having 19 windows open.
https://gist.github.com/ccampbell/9a0118b0e3e607ec56a3a2cc59...
WindowServer has consistently been the main culprit but occasionally other apps like to chip in where they can too. Often that means there isn’t one single process which I can kill to reclaim enough memory to continue working without being promoted again or having MacOS forcibly close all my applications on me. As a result, reboots appear to be the only real solution for me.
Interestingly though, in the past few weeks I have been working with similar numbers of open Sublime Text windows as yourself and I can confirm that since then, ST4 has been a regular and serious offender when it comes to memory usage in Activity Monitor.