HI, can we confirm that 10.5(2.15111.1) is the release that introduces the device type in CUCM to allow registration?
That information is included in the README, did you go through it?
Device pack 10.5(2.15111.1) does add support for Spark Room Kits, just as the release notes clearly state:
Add device enablers for Cisco Spark Room Kit and Cisco Spark Room Kit Plus
If you also check the linked bug, it shows an enhancement request for CUCM to add support for Spark Room Kits with device pack 10.5(2.15111.1) for CUCM 10.5.