Can't say about 15 ft wire without running the calculator. Likely, a lot amp-hours will be lost. Also, a voltage sense wire is a must in such a scenario because the run is too long.
Panels glued to rubber means he was not a professional. You can glue or VHB tape to fiberglass roofs, but not to rubber. Like Don said, brackets will stay attached to the rubber but will rip the rubber off the roof. EPDM rubber is very lightly attached to the plywood, a lot of air pockets under. They might stay put for a season, or 2, or 5, or they may fly off the roof next week, hard to tell.
