A 2hp motor will use 33% more power than a 1.5hp motor but it will only increase flow ≈8%.
So if the 1.5hp pump runs 10 hours for 1 turn over(because it's an easy number) then the 2hp pump will take 9hrs-48min.
The cost for the for using the 1.5hp pump is $3.00, the 2hp pump will cost $3.68.
I made up the turn over rate and the cost to estimate using round numbers. However, the one thing for sure is the 33% more power usage for the same amount of time with a small decrease in the amount of time.
Mike