Is this your scope?
https://www.telescope.com/Orion-SkyScanner-100mm-TableTop-Reflector-Telescope/p/102007.uts
A 15mm eyepiece would be right in the middle of what you have, so 26.67X. I think I would go bigger, to, say, a 32mm, or go smaller, such as 6mm eyepiece. A 32mm will give you...