Oh come on, the IS-2 isn't that much slower than the Panther Tank. Yeah, the Panther will beat it in a drag, but that's besides the point. The IS-2 is the fastest heavy tank in the game.
you might want to see the stats or play the game. Panther will circle IS-2 twice before it will do a single turn.
That is like saying SU-85 is as mobile as T-70.