Public folder functionality is broken in 15.19.1. It was scheduled to be fixed in 15.20 but Outlook 15.20 was pushed back for QC. You can revert to 15.8 or wait until Outlook 15.20.1 or 15.21 is released.
Thanks for the quick response, Any idea on timeframe for that release? I am starting to dread Outlook for OSX :(
FWIW Microsoft abandoned public folders internally a while ago. This was probably an honest to goodness mistake.
http://windowsitpro.com/blog/microsoft-turns-last-public-folder-their-internal-exchange-deployment
I don't think we'll see the requisite Outlook update until May but I might be pleasantly surprised. We rely heavily on public folders so I have held back from pushing out 15.19.1, though users are still free to get it from MAU if they want (we disable automatic updating). If they have a complaint about installing software outside of self service happy to roll them back to 15.18.
As per @Kaltsas said Microsoft has abandoned Public folders. In our environment all of our public folders (100+) had to be converted to full accounts and then their login access removed so the account acts as a shared email account. Once that's done the folder is added as a shared box.