Odd with that sort of setup I would be expecting a
lot better than that. I get about 25 fps at worst (bar the normal slow down at the start) and my setup is a fair bit older than yours. I do see it as low as 12 fps but that is nearly always the case when you first look at the fps indicator; for some reason it is super low for a few secs then updates to a more reasonable level. I always assumed it was getting an average before displaying anything. After that the fps seems fine (well 25 fps is not great) but you know what I mean.
SPECS: Ryzen 1700 CPU. Nvidia 970GTX. 16 Gig Memory. Win 10.