Make sure you have the patches required for your applications version and set the init paranmeters properly.
Interoperability Notes EBS 12.0 or 12.1 with RDBMS 12cR1 (Doc ID 1524398.1)
Interoperability Notes Oracle EBS 12.2 with Oracle Database 12c Release 1 (Doc ID 1926201.1)
Database Patch Set Update Overlay Patches Required for Use with PSUs and Oracle E-Business Suite (Doc ID 1147107.1)
Database Initialization Parameters for Oracle E-Business Suite Release 12 (Doc ID 396009.1)
bde_chk_cbo.sql - EBS initialization parameters - Healthcheck (Doc ID 174605.1)
We upgraded to 12c when TEMP_UNDO_ENABLED was recommended to be true and found in production we could not book orders, post journals or do just about anything. There were 200 sessions in enqueue until we set that parameter to FALSE.
You can get some improvement in performance and security by applying the latest PSU for your database release (188.8.131.52).
Thanks for sharing your experience.