Oracle upgrade from 11.2.0.4 to 12.2.0.1

We are preparing for upgrade from PeopleTools 8.55.14 to 8.56.05 and as a requirement we needed to upgrade the current Oracle 11.2.0.4 to the most current certified 12.2.0.1. After the testing upgrade we observe performance problems, that we can't figure out how to resolve. Applying all the PeopleSoft recommendations don't get the DB to the needed state. I created a SR with Oracle/PS, but it was closed without any helpful recommendation.

If anyone experienced such problem and found a solution, I would like to learn about it.

We are following the PS recommendations, but they don't help.

There are some init parameters that you may need to set.  Did you check the PS Init Parameters document?

Craig