I have noticed increased speed in geoprocessing between ArcMap and pro. Are the same increases apparent after migrating a python script using arcpy functions from the ArcMap compatible 2x version to the Pro compatible 3x version? I have a script that is working in 2x but takes a couple of days to run. I am trying to see if it is worth the hassle to convert it to 3x. I have started the process and keep running into issues getting the new script to run correctly.
I found that my arcpy 2.x script did ru faster in pro. Many times no tweaks were required. The exception would be if using a map document like CURRENT which would require changes.
As the others have suggested, it would help to know a few more details.