I added a pair of 15's last year, and have never even carried them. They are always the first optic cut from my loadout on every trip, I guess my style of hunting just doesn't constitute their usage. If I was hunting bigger country or smaller critters (Coues in AZ), maybe I would find more use for them. At the end of the day, I use my 10's on a tripod 99% of the time out to about a mile and a half or so, then I have my 80mm spotter for verification and detail work. I much prefer to glass with both eyes for sure, but I want the extra FOV my 10's give me for my hunting and glassing style (western hunting in canyons and draws where I rarely glass beyond 1500 yards)
Personally, I want to go to a compact spotter (like the small Maven or Kowa), and use that backcountry with my 10's. I think for my use case, that makes more sense than the 15's in the mix.