First, you'd never be able to re-sell it for anywhere near that.
Second, you will ALWAYS need to fix a bunch of things. Easily $2,000-$4,000.
This unit has the old green interior.
Original paint

Tires?
Looks like the original Coleman AC or maybe the Armstrong was replaced?
For $15,000 I would expect near mint condition including updated interior and a clean bill of health from an RV dealer AND mechanic. This does not appear to be there.
Doc Joe (winner) sold his 1984 270 that had a new fridge, new gen set, and was in great shape for about $17,500.
In my lousy opinion, $8,000-9.500 MAX. It's worth what you paid, nothing. Beat up ones and deals go for $5,000-$7,000 before the trip across country.
BTW: Where does that ladder go? Ummmmm.