I glanced at the ram graph a few times, didn't notice it go much above 8GB. Didn't play for very long in DX12 mode, but I'll have an experiment with it later on when I get a chance.
Also page file is on my Samsung 950pro.
It won't matter whether the pagefile is on your 950 Pro, as even the fastest SSD is many times slower than your RAM. But if it doesn't hit 10GB or go above, then it could be how Windows is managing your RAM..
What do you have your page file set to?