How long should a heat pump last before needing repairs

From the DFW comment, I'm guessing you implied Dallas/Fort Worth. If that's the case, then you'll have AC already installed, and a lot of winter days that are above freezing. For that climate, a heat pump would be much more efficient. The emergency heat setting on a heat pump is the same as what you already have and you'll want to use that when it drops below freezing. But all other times the heat pump will be more efficient.

In general the point is to filter your water. If you want to be sure about it, check the volume of your pool, and the flow rate of your pump. Run it long enough to go through that much volume 1-2 times a day. In practice, that's probably around 6-8 hours.

Make sure your chemistry is good, and then try it. If it looks nice for a few weeks, try lowering your operating time and see what happens.

As a side note, 1.5 HP is 1120W. That's probably peak power not normal consumption, but you should still assume it consumes somewhere around $0.10/hr or so.