I just got the new mini and this thing is using 5G ram for just the OS. ..
My 2014 mini would be using about 2.8G ram with same stuff open.
This comes up pretty regularly on Macintosh discussion lists. Someone finds that Activity Monitor is showing that their Mac is using a lot of RAM, and they then erroneously assume something like "the latest OS is a RAM hog", or that "there is a memory leak somewhere", or even worse, they go around telling folks that the standard 8GB of RAM that comes with a base Mac "isn't enough" and that they "need" to buy a lot more.
The above are generally all false. The Mac has gotten really good at memory management under recent versions of the Mac OS, and the Mac OS even goes so far as to often not let unused RAM just sit there unused. The Mac OS will notice that you have unused RAM and it will make use of it by caching things so that if you go back and use them again, perceived performance will increase. For example, if you open a folder with lots of items that all have to be rendered, it will be cached so that if you go back a few minutes later, it will open again instantly.
In fact, Under recent versions of the Mac OS, the more real RAM you have installed, the more RAM that the OS will use to cache things. So if you have 16GB of real RAM installed, it may seem as if the OS is using an outlandish amount of RAM if you glance at Activity Monitor. It isn't; it's normal.
The Mac OS now even actively compresses things in RAM to make real RAM stretch farther before your Mac needs to hit virtual memory. And, of course, if you have an SSD, even if your Mac has to resort to using VM, the performance hit might be unnoticeable. So, unless you are doing something that is incredibly RAM hungry, such as editing movies, 3D rendering, etc., 8GB of RAM should be plenty.