New is hosted on a better server, and obviously, OLD as the name speaks for itself, is the old, the first ordinary server they started SjSro with.
That explains the lag, and for the traffic, obviously when new started everyone moved there and shortly afterward they proclaimed the 'NEW' server as the server for 'foreigners', but as the time passed by, now both old and new are full of 'foreigners', there are barely any chinks.