We have two portlets that were destroyed during the upgrade to 15.5. Both of these portlets are copies of CA portlets. We created copies then used to copies to 'customize' them for our needs. The upgrade wiped out the portlets completely. When in the Admin side of the tool, and clicking on the portlet to see the definition, it returns completely blank and has and Error flag.
You will need to modify the custom portlets so the NSQL queries are not using the deprecated tables and are using the tables whose structure was changed in the new release correctly.