Apple Photos still does the facial-recognition grind. Can't be turned off, as far as I know, except by launching Photos.app, which pauses the processing. Or Terminal:It might also be the Apple Photos application making its database. I don't think it was available in Yosemite. I seem to remember it hogging the computer the first time I logged in.
Here's a relevant Apple page (it references Sierra, but I believe Mojave is the same).