I think 15" are going to require more space than that! As for the size of the box, the internal volume will be determined by the specs given by JL Audio. But yes, sealed boxes are generally smaller than ported boxes. Sealed boxes are also a whole lot easier to build and are more forgiving when it comes to making any type of mistake.LHSer said:Sealed takes the least amouth of room. Look to build a box with no more than 1 cubic foot per woofer and no less than 0.65 cu/ft per woofer.