Intel Iris Pro Graphics 6200

Hello, my question is: I have installed bootcamp with Windows 8.1 and I tried to use Pes 16. When I was trying to launch Pes 16, the program told me that I haven't enough video card memory even though I have an Intel Iris Pro Graphics 6200 (last Imac 2015); anyway the game seems to go very well but sometimes when the game seems to slow down. I think the game won't see very well the memory video card. Is it possible? What can i do to check? Do you suggest to put higher the video card memory from blu screen in Windows 8.1? (as i have written on a forum?) Thank you in advance.

Bye