Since your old pump is now toast, taking flow measurements is out of the question.
Ask your self this: "Do you think your pool needs more flow or less flow".
Consider the number of skimmers you have to run.
Also consider the number of pool returns you have.
What is the brand/model of your existing 1.5 HP pump?
What is the SF (service factor) of this 1.5HP pump? It should be stamped on the pump plate with the electrical info.
Is it 120 or 240v? How many amps does it draw now?
Is your pump located above or below the water level? How much?
What is the max flow rate of your filter?
Do you have a SWG?
Most likely you could go with a 1.0 HP Hayward Tristar Energy Efficient 2 speed model. You may even be able to go with the 0.75 HP model.
I use the Tristar 0.75 HP pump to drive water to an overflow spa/pool with about 7 water returns through 2" PVC. It also runs 2 skimmers and a pool skim. I have an oversized 520 sq ft. cartridge filter so not much head added there. My pool is 24000 gal. I run 10 hrs per day which is more than needed (long story). I have been very happy with it all. When I did my pool total dynamic head measurements I found that I got 90 GPM out of my old Whisperflow 1.5 HP pump and my new pump produced 80-85 GPM with only 0.75 HP. My old pump pulled 10 amps on the 240 volt and the new pump only pulls 7 amps which is a 30% reduction in electricity for almost the same flow.
My pump turns over my entire pool volume in 5 hours. I run 10 so I get 2 turns per day. I installed a flow meter on my plumbing to get a clear picture of all this stuff. The one I installed was made by RollaChem and less expensive ($35) than others. It seems to work fine.
Remember, if you go to the 2 speed pump, you may not need as much flow on the high speed because of all the turnover you have accomplished on the low speed. You only need enough water flow speed on the high speed to run your pool surface skimmers a few hours a day.
For MY pool Total Dynamic Head came out to be 50.
Attached is a file with the pump curves for the Hayward Tristar pumps. Also a WhisperFlow curve for comparison. I went with the Tristar because the pump curve/head combination worked better for my situation than the Whisperflow.
A model for you to consider is the Tristar SP32102EE dual speed with 1.0HP (1.85 SF) runs on 240volt pulling 8.5 amps on HIGH speed and 3.0 amps on LOW. I purchased my pump from
http://www.h20poolproducts.com. There price on this pump is $529.
Good luck
Lee