Yes we did similar upgrade. There are very few customers having Oracle Leasing OKL module implemented, so you might not get direct hits in metalink. The upgrade scripts run forever due to the volume of data stored in OKL/AP tables. you might have to work with Oracle support closely to get the scripts tuned.
Have a close look at the tables examples like OKL_CNSLD_AP_INVS_ALL and try to purge data as much as possible before upgrade. according to oracle some of the tables are not allowed to purge. Disable all customer code, triggers , custom indexes, and custom constraints before starting for the upgrade. allocate some flash drive storage for the upgrade.
If you possible can you provide more info or Oracle notes.