I consider 15% to be dry. The ambient moisture content in my workshop is about 15%, so even if I come by a piece of wood that is drier to start with, it will gain moisture to 15%. I doubt your cracks will move any more unless you bring it indoor unsealed and stand it near a radiator. but when you take it out to your workshop again they will close up.
If it were mine I'd turn it, give it the infill treatment if that's the route you've chosen, seal it, finish it, then bring it indoors to a cool room for a while and you'll probably be OK.