My current 2 bank charger is isolated, but only 5amps per bank and it's a Guest.
Is the proposed 3 bank, 15 Amp Charger, 3 banks of 5, 15 Total?
or 3 banks of 15, 45 amps total?
If a 3x5, 15 amp total charger, you might want to rethink spending the money to see only a marginal improvement in charging time.
With the ACR, it would make more sense to attach both banks of your 2x5, 10 Amp charger to the paralleled batteries.
Once they reached 13v, the start Battery, which likely needs little to No charge, will be paralleled in by the ACR and just receive a small topping charge.
Assuming the parallel, Non-Starting Bank is the power for a trolling motor;
If the goal is to get the batteries recharged during a lunch stop so you can make a second trip the same day, the 45 amp charger would be justified. Attach all 3 banks to the two paralleled batteries.
The 10 , 15 or 45 amp chargers will all get the job done if you won't be needing them till the next day.