CoD4 bandwidth and fixing it with the MTU . . .

CoD4 uses up a lot of bandwidth for me. When one person is playing every other computer on the network loses a lot of internet speed. We used to be able to play CoD4 on two computers at the same time, but seems like the bandwidth is too high . . . I was wondering if there's some way to fix this by changing the routers MTU rating? I have a DLink router at 1500 MTU right now . . . I was wondering if switching around the MTU helps . . . ?