Hello,
Chat isn't really the problem that causes the lag on survival. It is understood that many people do not like the ad system popping up on the screen and people most likely want a setting to disable it. However, in survival one of the more bigger problems that is making the server lag is by so many people coming on, using chunks, spawning mobs from grinders and so forth all around the land, making the server just a bit more laggy. I do hope that even though it lags you still find amusement of the survival gamemode. Dacon, Dylan and Purpz, has been working to fix the lag as fast as possible when staff report the server having another lag problem.