This comes up a lot and it's always an opinionated answer. I personally prefer my 15x56's because they're sort of a do-it-all for me such that I can often leave my spotter in camp. They're also really helpful at the range when you're pushing past 200-300yd - bullet holes are harder to pick out than antlers! But a lot of folks prefer a 10/12x + spotter combo.
I think a lot depends on what you do and your hunting style. I'm not a sniper and 250-300yd is my ethical max right now. Know your limits, right? But I'm also an elk hunter and my preferred terrain is mixed slopes and timber. I'm almost never in a position where I'm picking out an animal across an 800yd canyon and glassing him with a spotter for an hour before taking my shot. I'm more of a still-hunter, working over water and through timber pockets and modest sized clearings. Most of my shot opportunities average around 150-200yds. So a pair of 15's gives me "lots of glass" for my main use and "just enough" for the edge cases.
FWIW I hand-hold my 15's. Yes, they shake a bit more but I've gotten used to it, and I have a very tall trekking pole setup. I've found I can rest my elbow on the top of it to make an impromptu monopod if I'm glassing longer than a quick scan, and if you do a slow scan instead of trying to hold still on something it tends to minimize the effect of the shaking.
For times when I want to glass off a tripod, I have an Aziak ARCA mount. My tripod has an ARCA receiver as well, so I put the same baseplate on my spotter too. This means I can swap back and forth really easily. If I'm glassing for an extended period of time, I really like a good pair of binos over a spotter until I have something I really want to zoom in on. The wider FOV helps a lot with picking out things to pay attention to, and personally I find it less tiring. YMMV.
One downsize not often mentioned with bigger binos is that bino harnesses tend to mostly be sized for 10-12's. Make sure what you get fits your harness, or be prepared to upgrade.