It takes several battery cycles for the battery to get up to full speed. Your 1520 was probably the same way back when you first got it. After a half dozen full to almost empty (10-20%) cycles, your battery should last like the one in your 1520.
It's way too soon to say anything about battery life with any certainty.
My anecdotal experience has been great though. I took it off the charger at 9AM yesterday (Thursday) and it's still at 61% this morning.
Please do not compare the battery life to the 1520. The specs prove the battery life is worse. Stop being dramatic and comparing apples to bananas. Different phone. Different battery. Different hardware. Different screen. OH and different usage. I bet y'all aren't taking into account it's a new toy and YOU ARE IN FACT using it more than your old phone.
I think literally every new smartphone has a "my battery life is bad" thread less than 24 hours after the phone is released. Alternatively, I do not recall ever seeing an "OMG the battery life is amaaaaazing" thread in my life for any phone whether it is Android or iOS. Maybe the Turbo though, which it should, lol.