You can upgrade to Windows 10 with Symantec Endpoint Protection 12.1.6 MP1 or 12.1.6 MP1a installed, but you must first update Virus and Spyware Protection definitions to July 27, 2015, or later. Definitions as of this date include an update to the Eraser engine (115.1.1.10) that is required for Windows 10 compatibility
Endpoint Protection support for Windows 10
https://support.symantec.com/en_US/article.INFO2746.html