Bicycles don’t “vary in sizing”. There are sizes but they are meant for a specific rider size...or at least as a starting point. For your height, you need to be looking at a 15” mountain bike from 1984 to present. You are kind of at the soft point between a 15” and a 17” bike but you should probably err on the side of the smaller frame. A 17” mountain bike is designed for someone up to from about 5’8 to 5’10 and is proportioned accordingly.