Probably the best way is to do a backup of your catalog in Elements 15, then do a restore of the catalog using Elements 2019. During the restore process, you will be given the opportunity to select where your files will be restored e.g. your Pictures folder. Also, during the restore process, the catalog will be converted for use in 2019.
Alternatively, you can move your folders by drag and dropping them in the Organizer's Folders view panel.