After upgrading database from Oracle 11.2.0.4 to 12.2.0.1 serious performance degradation.

All I have seen a horrible degradation in performance after upgrading from 11.2.0.4 to 12.2.0.1 … High CPU usage, autotrace showing high values on consistent gets and plans are very different.

I have found the only way to solve this is to set the optimizer_features_enable=11.2.0.4 and then we are back to better performance.

The reason for the ask is this only a by-product of migration /upgrade and would this differ if I create a new skeleton db and data pumped in the data.

My overall goal is to figure out why this is and see if t here is an alternative to just setting it back.