I think the only issues on stock IS-2 is the weight itself against the suspension (torsion bar? or stick? anyway)
she will bouncing a lot when driving (light weight and hard suspension) compare with other Tamiya tank,
I think it cannot solve with stock parts. all you can do is either add the weight or adjust the (torsion bar/stick).

The metal track is mainly used for field run, not those well prepared battle ground.
I mean with small pebbles, rough soil, mud, it will give positive helps on driving.
Saw few time in previous game, Tamiya KT, Tiger I broken plastic track couple time in a battle.
I can say metal track is not a must, but it will help when you have field run.

Have a nice day!