I’m only answering my own question so that others may get some value from my experiences. 😉
I discovered that the ambari server postgres table ambari.host_version was showing a state of “UPGRADING” for one of my hosts”. I changed that to “INSTALLED” and then restarted ambari-server. Now the manage version is showing 15/15 and the upgrade process seems to be moving forward.
I only modified the tables directly as I verified the packages were installed and it was only a state problem. Hopefully this info will help others. Ambari needs to do a better job of check the /actual/ state of the servers and not solely rely on the contents of the postgres tables. I restarted Ambari server and agents and even restarted major components like the data node. None of that seemed to properly update the table, thus the need to manually modify it.