Microsoft has deprecated Transport Layer Security (TLS) 1.0 and TLS 1.1. Due to evolving regulatory requirements as well as new security vulnerabilities in TLS 1.0, Microsoft recommends that customers remove TLS 1.0/1.1 dependencies in their environments and disable TLS 1.0 and 1.1 at the operating system level where possible.
Dynamics SL 2015 CU1 and CU2 continues to have dependencies on TLS 1.0 and requires it for functionality of all of its components. If you are required to disable TLS 1.0 and 1.1, upgrade to at least SL2018C6 release for complete TLS 1.2 compatibility.