The only concern that I am aware of when using an oversized aeration system is that you may turn the pond water over too much/too fast and cause the water to get/stay muddier than you would like. With that said...a system that is too large can have some of its air released prior to getting into the pond. This dumping of air reduces the bubbles in the pond, reducing the turnover rate, reducing water velocities... which, in the end reduces the amount of sediments that get kicked up into the water column. You will be wasting some energy pumping air "into the air", but you will have a way to govern the end effects in the pond.
My opinion would be to look at piecing the system together with a smaller pump as its base rather than spending the money for a small kit that handles a 1.5 acre pond. OR, look into a decorative fountain. A modest size fountain will do a small pond justice when it comes to aeration.
