Ive been able to go through trainers from start to finish in less then 2 hours each. Not doing any story missions, and not trying to level up.
Equip every move they give you, and then go to a PQ and choose them for both allies. Do their moves as much as possible. If you have Super Saiyan, just keep spamming their moves. Also use their move as the finishing move as often as you can.
After you do a few PQs pause, go to player data and hit LB to see your progress bar with them. It should be moving up (small amounts every 2-3 matches).