Dell 7559 lag problem

Hi,

I've recently purchased the Dell 7559- it has an integrated video as well as 960M. Everytime i try to play a youtube video while playing a game my fps drops by half and the game gets really laggy. I suppose it has something to do with the integrated video, cuz otherwise the game runs smoothly. Is there any way i can fix it or disable the integrated video somehow?

Thanks in advance