thats totally normal, editor loads all kinds of things in the background.
What kind of things uses this much memory? The whole project takes exactly 4,42 Gigabytes on my hard drive. Maybe the editor loads the whole hard drive - “just in case”. Its terrifying. For sure.
try the suggestions here: Debugging and Optimizing Memory - Unreal Engine and let me know what is taking up the memory 
Maybe it comes from your code, specifically in the loading parts of it.
Or memory not freed ?
Nonetheless, a loop creating garbage objects (computing many times the same thing and adding it to an array for ex.) can easily take up all the RAM.
Well named attachment:)