Fans spinning up is normal. The game renders at 60 frames per second and it taxes the GPU (which is more than likely the integrated Intel one), because of the high resolution screen. It does the same on my Macbook Pro.
Counterintuitively, walking around and looking at the game world might be less taxing in lots of places, resulting in less fan activity. Not everywhere, though, so yes, if you play the game in full screen mode, the fans will spin up.
If it really bothers you, you can try playing in a window. Exit fullscreen and size the window to your liking. The smaller it is, the less taxing it becomes for the GPU. I think playing in 1920x1080 will let the fans rest.
