I'm pretty sure all iPhones after and including the 6 have the ability to charge faster when using an iPad 10/12w charger.
People used to swear their 5s charged faster too, until people pointed out it was pure placebo, as the phone didn't have the necessary hardware inside to draw higher currents!
It's not a placebo effect. What it is is not taking into account everything you are doing while charging. The 5s did charge faster because the ipad power adapters have enough wattage to both charge and run the phone at same time without reducing the amount of charge current going to battery.
If you turn phone off and charge you won't see any difference in charge time from the 5 watt power adapter to the 10 or 12 watt ipad power adapter.
If you have phone on, radios are working using current, display may be on, and if you are doing some processor intensive function, most of the current from the 5 watt power adapter is going to run the phone. leaving very little to charge the battery.
By using the ipad power adapters you could get as much wattage going to the charge circuit as possible for that phone. It's true it would not charge faster than components allowed. But it did charge faster than what was left available to charge when being used.
The current phones allow using more wattage for charging such that I see almost, but not quit, half the time to charge using a higher cpacity power adapter.