Are you two running stock ? Not rooted or ROM'd ?
I root my all Nexus phones before the plastic comes off out of the box, and start playing with ROM's within the first couple of weeks.
My point is, custom kernels and ROM's the few good ones at least, can really do wonders for performance and battery life. I'm talking night and day difference.
My wife and I both have a Nexus 6, and both running the very popular Chroma ROM. I get 5.5h Screen On this every day. I probably really get 6h On, but I plug on the charger when the red battery light alerts me of low % left, and that's typically around the 5h 30m mark.
On some bad days or crappy cell coverage days, some days I may only get 5h Screen On time. But thats been very rare.
Right now it is 8:00pm here in Chicago. I unplugged my phone off charger at 6:00am, so that's 14 hours, and mostly heavy workday use, hammering the phone all day long, with a million texts, tons of phone calls today, used GPS Navigation for an hour+, surfed the web a ton, e-mailing a lot during work, etc... And my battery right now after big use today; 24% left, with 4h 37m Screen On time.
But my OnePlus One blows the Nexus 6 out of the water in the battery life department. I'd guess by 1/3rd better.