Q: When I migrated from iPhotos to Photos, I lost all the albums and faces tags.

How did you migrate from iPhoto to Photos?

If you opened the iphoto Library in Photos the Faces takes should have been kept, also your albums:

see:  How Photos handles content and metadata from iPhoto and Aperture - Apple Support

If Photos did not migrate your iPhoto Library correctly, I would rebuild the iPhoto Library in iPhoto and then repeat the migration to Photos.  Did you update iPhoto to iPhoto 9.6.1, so you can run iPhoto on El Capitan?

Do you have the sidebar open?  If not do so with the Option+Command+S key combination. You albums will be listed under Albums at the left:

In the iPhoto Events folder will be albums for each iPhoto Event that was migrated to the new library.