After reading through some things here, I'm not going to request anything except for them to cease and desist. And with the warning that any reports of a 15yo debt, obtained from other agencies, to the credit bureau's would probably (since it would be reasonable to assume it's already been reported there 15yo) violate the Fair Debt Collections Act, and if that occurred, all sorts of agencies would be called into play: FTC, State AG, Lawyers, etc.
I concur - that's the best course of action for you.