I don't have a 6 anymore, but I'm pretty sure the 6 charges faster on an iPad power adapter. The 6s and 6 are not comparable for this. Maybe someone who has a 6s will run your code?
I thought the same. The battery on the phone has seen better days, so it might have been reporting 1% on the first test when in reality it still had a bit of charge.
My 6S+ charges about 20 minutes faster on the iPad Air charger then it would on the charger Apple included with it. Those are about the same results you would find on the YouTube tests using the Air charger.