The outdoor UV sprays are made for deck cushions, umbrellas and things like that, canvas weight fabrics. They are not suitable for quilting weight cottons and would leave your wall quilt quite stiff and possibly damaged. The fine art sprays are meant for hard surfaces like oil paintings, colored pencils and pottery. All of them are merely UV resistant, not fully blocking, and for fabric in direct southern Texas sunlight that likely will not be much help.
Better to go with a window filter or find another place to hang your wall quilt.