So CLL isn't correcting enough to get back to target? What is the Lambda fuel trim at that time? Is it just hunting between target and 15.1 or just drifting up and settling at 15.1?
I would turn of CLL, tweak your IAT fuel comps to give you the desired stable AFR, reactivate CLL. Log, repeat.
If you are using the default values for IAT correction it says in the notes that the correction may be more than needed and require a tweak.