2015 MBP w/Retina, 8 gigs RAM, SSD. I'm one of those folks whos Mojave install brought the machine to a complete crawl. Extremely unresponsive. And wifi hardware not detected.
I had to restore High Sierra. But...the photo library got effed up. I don't understand how, but...after I restored my High Sierra backup, I haven't been able to open up Photos because it's telling me my photo library was created with a newer version of Photos and I need to upgrade before it will open it. This is from the High Sierra backup I did immediately before installing Mojave, so I don't know what went on there.
Interestingly, on the Apple forums a lot of people are having this exact issue with various models, and more than one person said to allow about nine hours for your partition to erase and restore. Took mine only two! Most folks say that Little Snitch is the culprit...except I never had Little Snitch. Ever.