Internal code name was Threshold 2. To be able to make a difference between the builds easily (beside from internal branch builds and Insider Builds) you can check the version with winver.exe
With the new Windows as a service methodology there is a new need to differentiate the builds.
Version is now written as last 2-digit release year and last 2-digit release month. In this case 1511 is equal to 2015 November.
