I own a Zenphone 2, and (as this test showed) it does charge very fast when hooked up to the included powerbrick. But when it is hooked up to a "regular" brick or a PC USB port... it charges V E R Y S L O W L Y.... if at all. So keep that in mind.
Hang on. From the test, it seemed like you used a QuickCharge brick with the LG G4, even though the G4 doesn't come with one. Therefore, a real-life owner would need to buy the charger separately.
On the other hand, from your description it seems you used the 5 volt/1 amp (NOT 1.5 amp) brick that comes with the iPhone 6. However, the iPhone 6 will charge at a quicker rate if you use the 5 volt/ 2.1/2.4 amp iPad charger. Why didn't you test it with one of those?
We discussed taking into account the runtime of the phone on a usual charge, but we ran into issues. A lot of things affect how energy is consumed by the phone (including the mentioned heat or cold). In particular we've noticed that carrier choice actually affects battery life.