Need review of what horsepower does on pumps.

I have a well, 29' below where the pump will be. It now has a 2hp Sta-Rite
pump on it.

I'd like to put a 1.5hp Sta-Rite on it, because of economics.

Does the HP of the pump relate to how much suction it has, or does it relate
to the number of sprinkler heads I feed with it?

If it relates to number of heads I feed with it, I know I can get by with a
smaller number of pump HP. I have 3 sections of 4 heads ea.