Which Hayward pump is equivalent to a 1.5HP Pentair Whisperflo Pump?
Why is that relevant to a new build?
How did you decide that that would be a good choice for a pump?
The right pump depends on what the pump needs to do.
The best way to choose a pump is to determine the system curve or system curves for various configurations of the system and then determine the flow rate required for each system configuration (for example, solar on vs. solar off would be a different configuration with a different system curve and a different required flow rate).
Once you have a graph of the system curves and flow rates, you plot the pump performance curves for different pumps or curves for various speeds of a variable speed pump to see if the intersection of the pump curve and the system curve (called the operating point) is in the part of the pump curve labeled as the best efficiency range (typically in the middle third of the pump curve) and the operating point needs to be at the required flow rate.
In any case, the pump should be a variable speed pump. By going with a larger variable speed pump, you should be able to meet the needs of most pool systems unless they are unusual.
For most typical pools, a large variable speed pump will usually work.
What are the details of the new pool?