Alienware 15 R2 - games,stuttering

I have an Alienware 15 R2 laptop with nVidia graphics built in. The laptop is connected to a Dell D6000 dock via a USB C cable. My Full HD monitor is connected to the Display Port port on the hub. 

When playing games, the games appears pixelated as if it is running on the Intel GPU and not nVidia dedicated GPU. 

Any idea why this is happening. Should I connect the monitor direct to the laptop instead of via the Dock?