Zach is spot on. There's no reason to rule out a 15-year-old molded fiberglass trailer, but there is reason to do a careful pre-purchase inspection.
A few suggestions about that... (1) Download, print, and use the Buyer's Checklist
(from the Document Center in the "More" tab). (2) Take a friend, relative, or neighbor with RV experience to inspect the trailer with you. (3) Pay a nearby RV repair shop to do a pre-purchase inspection. Unless the seller has a long line of buyers waiting or something to hide, they will likely cooperate with you on the inspection.
Two things I would be most concerned about... (1) Appliances. They can be expensive to replace. Test to make sure they work. If any don't, that should be reflected in the price. (2) Leak damage, especially in the floor. Bigfoot has a plywood subfloor and furring inside the walls and ceiling. If a window or vent has been leaking, there could be mold and/or rot. Feel for soft spots in the floor, tap around inside lower cabinets and benches, and look for any staining around windows
and roof vents (a little from condensation might be considered normal and acceptable).
Molded fiberglass has a distinct advantage over many other RV's in that there are no seams and corners on the exterior to develop leaks
. That's one reason a 15-year-old trailer is worth a closer look.