As far as I know ML2 and ML3 use the same common source libraries for scanning so psycik will need to explain this difference I have been working on this particular problem over the last two days and I've reduced the scan time for my 5800 track sample from 8-9 minutes to about 6 minutes and I hope to drop that further.
That was just a difference from the scanner from ML2 version 7.2 and the new one for version 8+, this version added some other play list mp3 loading options and I think that slowed things down quite a bit....
Once it's done that first scan though it only looks for changes so it will be a lot quicker.
Gigabyte AMD A8 Brix, 4 Gb DDR3 Ram, 120 Gb SSD, Samsung LA46A650 TV (HDMI), Harmony Remote 525
Windows 10 Pro, NPVR 3.5.7, AC3Filter Client
Windows 10 Pro Virtual Machine SiliconDust HDHomeRun Dual DVB-T with NPVR 3.5.7 Server
1 x Roku3 with Plex, Plex Plugin, NextPVR Channel for Plex
I just redid the SQLite logic a bit so there should be a huge difference in Full Scanning speed. I went from over 150 ms per file to about 50ms.