Two 1.5" bulkheads just barely gives you more surface area than a single 2". A 2" equals 3.14 square inches and two 1.5 " combined only equals 3.53 square inches. With the additinal fittings required to plumb the two together you might actually be better off with a single 2". Every elbow, inch of pipe length and valve adds a head restriction while a straight short run of 2" adds very little resistance. A single 2.5" equals 4.9 square inches and a single 3" equals a whopping 7.07 square inches.
Just something to think about.