Many Android phones have a feature that allows for fast charging, often referred to as Qualcomm Quick Charge or, in Samsung’s case, Adaptive Fast Charging – there are others.
These phones have special code usually located in a chip known as the Power Management IC (PMIC) that communicates with the charger you are using and requests that it send power at a higher voltage.
The iPhone 6 doesn’t feature fast charging, but its Qualcomm PMIC is smart enough to recognise when you use a higher-amp charger (like the one you get with the iPad), and that’s a good thing because fast charging will heat up that Li-ion battery and cause it increased wear and tear.
For the same reason, you should never leave your phone in a hot car, on the beach or next to the oven. A hot battery will suffer long-term effects on its lifespan. And so will a super-cold one, so don’t leave your device in the freezer or out in the snow.