Lightroom 6.7 just keeps getting slower and slower on my Mac (10.11.6). As I write this, I'm waiting on an import (an Add, actually) of 585 RAW files, each about 15 MB. I'm making 1:1 Previews and Smart Previews. It's been over 30 minutes and about 200 images have been imported with the two previews.
I have a 1 TB HD on my Mac and it's 50% full. Graphics processor acceleration is disabled.
I would love some help on this.
By your numbers that is 9 seconds per file.
Not great speed, but the smart previews + 1:1 previews are certainly slowing you down as that is a lot of extra disk I/O.