when you have the phone plugged into a usb port on computer to charge (I do this at work) it says it will take 4 hours to go from 74% to 100%. I know when I did this with my iPhone 5 it didn't take that long. Where as if you use the charger that comes with it or one rated at 2.1A it won't slow charge and goes a whole lot faster.
What I'm wishing is that it wasn't as slow when plugged into usb on computer, but obviously not as fast when plugged into wall charger.