Context is key but floating shelves in a kitchen (especially next to a range) is typically a terrible option.

The only thing worse that floating shelves next to a range is glass shelves next to a range, and the typical underpowered vent, with no make up air system. People don't realize the CFM required to keep their kitchens clean. Or that they also require make up air.

I think 15" (and probably 18" too) is so small I'd just skip it. Rather than look airy and cute they will chop up your walls in an odd way

My vent power is fine- vent is wider than range. Why is this a terrible option