I have a 3-15x and the glass is completely fine for anything I will ever do
I do like the 3-9 better, it’s a little more forgiving throughout the upper end of the zoom range (duh) and I prefer having no paralax adjustment for my use. The 3-15 has a new role now, the optic I need now is either a 3-9x swfa, another small nightforce or something similar, because I want easy and forgiving because I am going to put together a rifle for my daughter
I may keep the 3-15 for something in the future or may sell it to fund a scope for the kid, probably something with fixed parallax and 3x zoom range for eye box forgiveness
I think overall the 3-15 is a great versatile scope, but I do appreciate the simplicity of the 3-9x and that’s plenty of magnification for me