Weird stuff the last two or three weeks over here. My wife and I play BO2 together online and recently, when we play split screen, the lag is terrible. We get pauses in the action, disconnected, etc. However, when we play just one person at a time - it hardly lags at all.
I have a 30MBS download speed and nothing else in our system (computers, netflix, etc) seems to have issues.
Only idea I have is to never leave your wife! Got yourself a gamer?! Well done