I'm not so sure about the rookie part. Tigers were as a rule to tough to be destroyed - AT put them out of action and they were too heavy for their carcase to be easily pulled away, but that meant the crews had not so bad a chance of survival.
As to the IS-2, well it had a heavier gun and thicker armour - as it had been developped to fight the Tigers. It was also faster, lighter hence more manœuverable and had greater autonomy. ( the autonomy problem was the reason a good many Tigers were destroyed while aboard trains… ) Its turret was only built for 2 people however and not 3 like the Panzers, which meant it shot far slower, also its optics were inferior hence a lesser range but its armour negated that problem… also its ammunition rack was far too small. I believe what claimed the greatest number of them were the Panzerfaust, until the Soviets learend the hard way they should keep an infantry screen around them and make it clear the terrain.
That germans suffered form lacking crew training was a fact from 1944 (and especially in 1945).
Of courss an IS-2 would be more or less lethal to a tiger at close range, but seriously. gettting that close to a tiger without eating 8.8cm was REALLY hard, if not impossible unless you greatly outnumbered it. This was mostly thanks to the lazer presicion in the infamous 8.8 L/71 combined with great optics and a good prenetration. You didn't do a frontal charge on a tiger no matter what you were driving.