I would steer clear of 15x binos for antelope and open country deer hunting. 10x are great for spotting and 60x spotter is great for field judging and spotting game in thicker brush. The name of the game for antelope, deer, and other game is field judging bucks. You''ll soon find that 15x isn't enough power even with a doubler to field judge game where inches make or break a score. As an example, could you tell if an antelope buck has 6 1/2 or 7" bases or 1 1/2 or 2 1/2" 4th quarter circumference at 800 yards with 15x....no way! If you are an experienced antelope hunter you can actually tell mass measurements at that distance with a spotter. Can you even see brow tines on a muley buck at 800 yards with 15x? When a 8 1/2" billy mtn goat is ok and a 9" billy is big you better have a spotter to tell the difference! Maybe score doesn't matter.....but if it does I'd steer clear of 15x and invest that $ in 10x plus a spotter.
Where 15x shine is in super brushy country where everything looks similar and you spend hours and hours trying to spot animals. It still requires a spotter to field judge them. There are very few situations in Colo, Wyo, Utah, and Nevada open country hunting where 15x are going to help you more than 10x binos plus spotter. There was one instance on a bighorn hunt a couple seasons ago when 15x would have helped. Rams were always in a 2 mile long section of cliffs/rock that all looked similar. I was across that canyon glassing. My 10x was to little power to spot rams blending into the rocks and my spotter took to long to cover the area. 15x would have worked perfect for that one canyon. The remainder of the unit the 10x plus spotter worked perfect. I don't hunt cows deer in Arizona....and can see where that would be the place for 15x plus a spotter.