Hello, newbie here, and I'll admit at once that I know nothing about coins. But I inherited a collection from my grandparents, among them a 1922 Peace Dollar, that's had a pin soldered to it, and has been worn as a brooch. It also has initials engraved. I assume that means its value as a collectors item is zero?
It's worth at least spot value which is at the moment about $12.50....but like Slacker said, I'm sure you'd get a couple of dollars more for it. About $15 sounds reasonable if you're selling it, especially if the pin is silver as well.