Stock units vs IS-2

So this game my opponent went for T2 into IS-2 call in with shocks, I built all Tiers as ostheer, the first IS2 went down to a stug backed by pack 40 supporting a retreating p4 that had engine damage.

The second IS2 survived and took out my stug because the flame arty makes the game in my pc really slow even had the disconnect and then game speeds up too catch up and i lose stug and pack.

Later on got t4 and went for panther, opponent got a second IS-2 and again the flame arty to decrew my packs, there was a moment were it looked like I had lost the game but my opponent didn't kill the decrewed packs so that allowed me to come back plus the IS-2 take a long time to repair compared to my panther.

I was retreating back after attacking the IS-2 being repaired one had engine damage so my opponent chased my panther with only one my packs were going back to base and managed to get there just in time to take out the IS-2 and I got a vet3 panther from that engagement but my opponent gave up after that.

I took a long time to choose a doctrine then decided to get g43 to fight the shoks rather than the tiger, everyone uses tiger I like to try different stuff.

The flame arty is really strong even though I would keep my packs separated so the arty wouldn't get both it would decrew the pack without chance for escape.