Im having this same problem too. I've even restarted the phone after a full recharge and with no apps running and usage time will always be 20 minutes out of very hour standby. Therefore the usage statistic is not in the least accurate as to how long I've been using the phone. I have noticed this since ios8. I used to think it was the ⌚️ constantly communicating with the but I have discounted this (leaving the ⌚️ off and Bluetooth off too). I have background refresh off and all other settings disabled too. The only time usage doesn't seem to clock up is when I place the in ✈️mode. Perhaps it's the looking for a signal from a cell tower. Nothing else seems to make sense. Just my thoughts. Would love to have a solution to this.
Sure sounds like a cell signal issue but that shouldn't effect your usage time. I also have an AW also and my 6s isn't acting up. I currently have 48hrs. standby, 6hrs. use with 60% batt.remaining.