The 1.5 hp is probably plenty, this link for the main pages goes over the pump size. Usually a pump is sized plenty big but the filter will be off.

http://www.poolsolutions.com/tips/tip83.html


If that is a link to the company that installed the pool, have your tried asking them the volume. Otherwise, it's a case of diagramming and measuring the depths in your pool to get an idea.

You can also search the forum on 2-speed pumps, which are recommended to help electric bills.