That's what I thought to try: playing Skorpion G and/or Defender.
About doing 13 from 15: if this mission is hard and almost impossible to do for players like me, then the future missions will be harder, not easier.
Defender would work as well. Maybe even a bit more forgiving with the alpha + armor.
It is definitely not impossible, for anyone with a tier 8+ tanks for that matter. Don't cut yourself short. If high tier - play aggressively; low tier - play conservatively and as support. IIRC the average game length is +/- 7 minutes, if you die early switch over to the skorpion. Rinse and repeat. I bet you will finish this mission much quicker than you expect.
G/L w/ your missions!