I doubt that there could be any straight forward answer to this. You can try below:
1: dump the 'get session' output 2-3 time during the busy hours, put them in excel sheet etc and check which policy are used.
2: Enable the policy counting only for the policies which are not in the get session output. Also, if you have the traffic logs enabled then you can see which policies are majorly used. Enable the counting accordingly.
3: If number of unused policies are still more than 125 then you may need do it in phases.