Actually, your 1.5 HP pump is an "Uprated" model so it is really a 1 hp pump. (Full rated, max rated, and up rated is a game the manufacturers play to make their numbers look better and prices seem more competitive. However, pump performance curves are really what tell the story, not HP. Your brake HP is 1.65 which is the same brake HP that a full rated 1 HP pump would have. A 1 hp pump is not unreasonable on a 150-175 sq ft cart filter. The filter is oversized for a pool that small but oversizing carts is considered good practice since it gives you a very long mean time between cleanings. my pool is under 7k and has a 150 sq ft cart and a 1.5 uprated pump also.

A 2 speed pump would have been a a better idea when the pool was built and your cheapest upgrade would be to install a 2 speed replacement motor on your exisiting setup.