I would guess that the small size is way too small, but you might want to take it for a spin to check it out.

I guess it would depend in part on how that 5 ft 10 in is distributed between your arms and torso and legs. I believe they call that a medium large which would make sense for someone of your height on paper at least. The 15.5 is a small which would be kind of ridiculous if you think about it.

I think that bike will be way too small for you. I'm also 5-10 and I would ride either a ML (18.5) or L (19.5) comfortably. The reach on a S is only 420mm which will feel like the bars are in your lap. It also only has a 100mm dropper which could be a problem. Wheelbase at 1144mm is pretty short too. I'd wait for something that fits you better.

For reference my trail bike has a reach of 475mm, wheelbase of 1247mm and 175mm dropper. XC bike has a reach of 460mm, wheelbase of 1194mm and a 150mm dropper.