You may see some of the previous texture through the sprayed texture. As Steve said, if the surface is painted with anything other than a flat paint, you'll need to prime it with a primer that is suitable for the purpose. High gloss paints need a primer that will bond to glossy surfaces.
I've been known to use wallcovering "border adhesive" or whats known as "V.O.V." adhesive to bond a new texture to a glossy surface. It works pretty well, especially a sprayed texture.