Hi. I had a 1940 burb I sold about two years ago, when I lived in Florida. Moved to Texas because grand kids and wife. Had it up for sale for 7000. Sold it for 2500 I think. I\It was it was a driver. Had everything except front bumper and two rear seats.
Wished I still had it. $15000 is a lot for what your post reads.
take a good look at the roof should be solid, no holes. the back of that burb looks like steel but is really wood and steel. rear inside, where windows go, is wood frame wrapped in steel. rear window inside is wood frame insert. tail gate is wood frame inside for support. The one I sold had main body done. all wood repaired wood window molding deck with new bed strips. needed fenders running boards reworked and hood repaired. All in All I had around $12000 into it. I figured around another $20000 to finish it. Suburban's are more expensive to restore. $6000 or $7000 I would say tops. At $15000 it should be complete truck no missing parts. At that kind of money you can buy a daily driver not a 40 burb but 50s 60s 70s truck. Only reason I can think is 1028 as I remember 40 burbs made. I would walk away if he will not go lower. Take a good look again at it Make him an offer leave your name and number with him. Hope this helps. Jbennett