For what it's worth, did similar journey, but with different brands.
Love my ZEISS Conquest HD's 10x42. Liked 'em so much the 15's of them. They're very cool as well.
For the specific places I'd like the 15's with me, I'm cool with bringing 8's for handheld.
However, some steep Alpine places, Hoofing 10's + 15's, just didn't make sense, for the weight, and I like having binos in chest harness for quick hand-checks on-the-fly. No way you're doing that, any kind of well, with 15's, doing hand-checks that is.
So... looked for a straight spotter (so wouldn't have to re-adjustment tripod hardly at all when switch from binos to spotter), have settled on a used Maven S.2 the 12-27x56mm one.
The 10's and the S.2 are a good sweet spot. The other spotter I'd picked up used first, was the ZEISS Dailyt the 65mm, whose picture is better (quite good), but the extra weight in steep Alpine terrain wasn't appreciated. Hence bumping down to the more Ultralite-style S.2 Maven.