I'm with the same problem since I bought the game. (http://forum.game-labs.net/index.php?/topic/10378-low-performance-on-nvidia-gtx-960/?hl=performance) But no answer. A lot of people with Nvidia cards have this problems. I've met 1 guy with a 960 with 1fps, other guy with 970 with 25fps... this isn't normal.
With a 2016 Mid-High PC, this game must be playable.