To estimate the horsepower required for a 1500 GPM fire pump, we need to know the required pressure or head against which the pump is operating. In fire protection systems, the pressure requirement is typically expressed in terms of pounds per square inch (PSI) or feet of head (ft).

Without the specific pressure requirement, it is challenging to provide an accurate horsepower value. However, as a rough estimate, a fire pump with a flow rate of 1500 GPM could typically range between 200 and 500 horsepower.

It's important to consult with a fire protection engineer or refer to the manufacturer's specifications for the specific fire pump model you are considering, as they will provide the accurate horsepower requirements based on the desired flow rate and pressure for your application.