P3015 error but no P0A80 after module replacement.

If you let the battery sit for a week, you'll be able to identify the bad module in block 5. It's self discharge speed will be much faster than the good modules. Voltage readings doesn't have much meaning to these modules.

 

Well you can replace both and let the 2 sit. The bad one will start discharging at a high rate.

You would then have to balance your entire pack or it'll surely fail again because of all the modules you've changed

 

It's important to find the weak ones as they will pull the good ones down to their level.
On discharge = weak cell does no work leaving it to the others.
On charge = weak cell either can't take a charge or gets hot "a short", in either case the better cells take a beating as the system keeps charging trying to attain desired total voltage in spite of a dead horse in the yoke.
In the case of a short voltage on that one cell is attained quickly making the total charge voltage low so the good ones never get a full charge as the shorted one steals the current overheating all cells nearby.

To properly rebuild a battery is very "very" time consuming without many chargers and a good supply of cells to pick from to match with.

Doing it the way you're doing it you may squeeze another 20k out of it but if done properly you may get over a 100k.