has anyone tried to quick charge the iPhone 6 s?

The phone itself controls the actual charging, as do all devices conforming to the international standards for SMART Lithion ion/polymer battery devices. While a power converter that puts out too little power can impede that built in system, giving it more power than it is designed for does nothing as the phone itself will regulate what the charging system actually uses.

Just beware that frequent deep discharge cycles will cause a lithium battery to decay much faster than more frequent charging and shallow(er) discharges will.

USB power on an Apple computer is hardware/firmware controlled, not controlled by the operating system? See Apple Computers and Displays: Powering peripherals through USB - Apple Support

The power adapters sold with iOS devices have nothing at all to do with the charging circuits in the device. They are simply power supplies, and the device itself, as I said, controls charging. OS X does not enter into this whole discussion at all.

iPads have always supported charging at 2.1A so their power adapters support that output. The iPhone power bricks are limited to 1A because prior to the iPhone 6 no iPhone supported charging at at more than that so there was no point supplying more power as an iPhone 5s or earlier would only use a max. of 1A for charging anyway. That was why you can charge any iPhone with an iPad power supply, as the phone will limit charging to 1A regardless of what I put you give it.

Charge your iPhone 6 or newer with an iPad power supply and yes, they will use the full delivered 2.1A for charging. But it has nothing to do with OS X at all. It has to do with what the Phone and SMART battery pack are design-limited to, and what the power supply puts out. If a power supply puts out less that the limit built into the device's charging system, then it charges slower (which is why an iPad charges slowly from a computer's USB port versus its power supply). If the power supply puts out exactly the maximum design-limit of the device's charging circuit, then it will charge optimally. If the power supply puts out more than that maximum internal design-limit, the device will NOT charge any faster as it will not use more than its built-in maximum regardless of what input it has.

Spot on, was facing the same issue, upgrading to El Capitan resolved it

I had always heard that it was best to let a phone battery power cycle once per month to make sure that it did not develop a memory state.

I had always heard that it was best to let a phone battery power cycle once per month to make sure that it did not develop a memory state.

That was true with old cell technology. Current lithium cells do not suffer from such memory. A deep discharge will cause more harm but the phone will not let the batteries get that low before they power down. Just use the device, charge when necessary and don't worry about the batteries.

As Raymond says, that only applies to older battery technology, particularly NiMH. SMART Lithium ion and polymer cells simply don't face that same problem and it's completely unnecessary to condition them by period deep cycles.

Very good summary Michael. Thank you.

(El Capitan?? Really???)

For charging my old iPhone 5s and newer 6s I use portable power bank (10 000mAh). Charging current is about 2.1Amps. Measured by Mastech MS8229 on cable.