What about the CCS 15.0 and CA1 12.6 compatibility ?
On the Product Information Bulletin of CA1 12.6 can be read:
CA Common Services for z/OS Prerequisites:
Before you install CA 1 we highly recommend that you install r12 of CA Common Services for z/OS. Minimally, you must have r11 of CA Common Services installed at the SP08 Service pack before applying this product package.
The support of CA1 12.6 has been ended on July 29th, 2017, the compatibility CA1 12.6 and CCS 15.0 wasn't tested.