Windows 10 build 16299.15 is the RTM build of the Fall Creators Update and it was released to Windows Insiders in the Fast Ring earlier this week. Today, Microosft rolling the update out to Windows Insiders in the Slow Ring, and we’ll also get the official ISOs for build 16299.15 sometime soon.
Build 16299.15 is the build Microsoft will be releasing to regular users once the update starts rolling out on the 17th of October. Build 16299.15 is also the last build of the Windows 10 Fall Creators Update that the company that Windows Insiders will get. However, Microsoft will release patches for the build to Windows Insiders in the weeks before the rollout of the Fall Creators Update starts.