Even if a driver is said to be 15" it won't be exactly that size. Thusly, you will need to measure the specific driver you are planning on mounting and then build a jig. The easiest way I have found is using a plunge router with a self-made jig or an item such as the Jasper Jig (works well, but is made of a brittle acrylic material). A product such as this allows for easy, accurate, holes in a variety of sizes for a fairly good price if you don't want to make yourself a jig. This method will also allow for flush mounting of the driver which a jigsaw would not allow.I was just planning on cutting it out with a jig saw but need to find a template or something to make a pattern to follow? any suggestions?