Given that you have a spa and a waterfall, I suspect that you would not want to downsize the pump. In fact, an uprated 1.5 HP pump is pretty small for a spa. Are the jets working ok?

One option would be to replace the motor with a two speed motor. Running on low speed is fairly efficient for just circulation but you still have high speed for the spa and waterfall. If you go this route, make sure you replace the seals as well.