I haven't had any issues with standby drain on my 6, I have mail set to fetch hourly, background refresh is off. I tested my iPhone 6 awhile back, I have pretty bad LTE in my house, about -115 to -100 with field test mode enabled. I let my phone sit overnight connected to LTE with WiFi off to get the maximum "Low Signal" drain and my phone was at 100% when I left it, and in the morning it was still at 100% I believe.
I don't get many notifications, usually 3-4 max over the course of a night, so yeah. If your phones are blowing up with notifications that would explain it. Otherwise, try a hard reset, try a reset all settings, and if all else fails, set the phone up as new.