Hi,
I did that actually but to no avail.
So since that and repairing the library did not speed things up, I tried something bit more radical: I created a completely new and empty photo library, then downloaded the entire library from iCloud, about 800GB.
Alas, it did not speed up the People album.
Same behavior as before - when I click on People, I get the beachball and ~30 seconds later the people thumbnails load.
The large slideshow image just shows gray and the person's name.
If I click on play the slideshow, it actually plays it and when I stop it, the gray card with the name reappears.
Other than this behavior, Photos works fine.
There is no delay wen clicking on any photos or other albums, just the People one.
It's rather annoying and I just don't understand that.
Now, since creating the library from scratch on the Mac, I can say there is one other anomaly I can't explain, the counts are different on my iPhone, Mac Mini and in iCloud:
Phone: 68,831 photos, 6,770 videos
Mac: 68,832 photos, 6,770 videos
iCloud: 68,828 photos, 6,770 videos
What is really weird is there are 4 more photos on the Mac than in iCloud, even though the Mac downloaded all its photos from iCloud into the new, empty library I mentioned before via Settings/iCloud "download originals to this Mac".
*sigh*