I have about a hundred Cisco 7960s on 3cx v14. I spun up a 15.5.2 test box in preparation for upgrade, but I have been unsuccessful getting a 7960 to register on v15. The article (https://www.3cx.com/sip-phones/cisco-7940g-7960g) refers to Cisco firmware versions that are applicable to the 7961 - not the 7960. The latest firmware for the 7960 is POS-3-8-12-00 from 2009. Anyone successful getting 7960s to work with 15.5.x? If so, any tricks you encountered different from v14 registration?