Naxxramas 25 Man is the only thing on Laughing Skull US that is lagging, 10 man, and the other 25 mans are fine, but Naxx is a lost cause at the moment. :-X
I'd venture to say that the 25 Man Naxxramas server is just being overloaded by an abundance of people doing them. Since the 25 and 10 Man servers are different.