I just did R2 7-star with Palp(L), Thrawm, RG, TFP and Tarkin. Except for Thrawn, they are crap geared, as you can see:
https://swgoh.gg/u/lantador/collection/?f=empire
Key (for me): Stunlock/fracture R2, kill Han, Luke, Leia as fast as you can, kill R2, leave Ben and Chewie for last. I needed 5-8 tries for good RNG in the start (ie., you dont want Thrawn or Palp stunlocked out of the match the first rounds, till you can get your fracture/stuns rolling).
When I got the first two DPS (I killed Han, then Luke) out of the picture, it was smooth sailing. Use Thrawns protection-heal wisely, and keep the defense up from RG up - even if it means you lose him (I lost him right before I killed Luke).
The fight is all about control.
Good luck.