The Photos.app has many different tasks to complete, when it is analysing your library, and the scan for faces is only one of them. For a library as large as yours it may take several weeks, and Photos does not update the status line showing the progress regularly. For my Photos library with just roughly 60000 photos and videos it too more than a month, and then the status message jumped from 0 photos scanned to 710 people within a few minutes.
While you are waiting for the first people to appear, you may want to check, if your Photos Library is containing items that cannot be processed by Photos. Items you imported before the upgrade to macOS 10.15 may be in a format that Photos can no longer process, because the system does no longer support the codecs. Such items can block. the face recognition. You may want tockeck all videos that are not using the HEVC codec or H.264, if they can still be edited. And look for older image formats.