I have both sitting in front of me now. Excuse my following ramblings, I hope it makes sense.
I am using my red box 1005 intellicharger to individually charge each one of my batteries. They are all currently resting at 12.7v, about .4v lower than they should. I have the PSC60 that I usually use to charge them when I have all 11 bussed together here as well. When I put it on just 1 battery, it charges for a few minutes and says it is full, but when I put the 1005 charger on them, it is actually giving them a full deep charge.
The plus to the PSC Charger/Power Supply is the Power Supply and Recovery Mode. I use 2 PSC60 in Power Supply Mode on my test bench when I am using the amp dyno to supply a little extra current and to keep the batteries fresh.
Recovery mode is great when you have a dead battery. We were able to recover a D6500 that a customer has let get down to 9.5v. After running recovery mode on it and giving it a full charge, the battery was back to resting at 12.9v.
Personally I would go with the PSC15 if I had to choose due to the extra functions you get.