Microsoft is rolling out the final build of the Fall Creators Update to Insiders in the Fast ring today, which is packing new bug fixes and changes. This is the final build, also known as the Release To Manufacturing (RTM) build, which means from here on out Microsoft will be servicing build 16299 with cumulative updates and patches.
The Fall Creators Update is pretty much done at this point. From here on out, Microsoft will be fixing any last minute bugs via patches installed through Windows Update, rather than using full new builds. 16299.15 is the last full build Insiders will receive for the Fall Creators Update.
With build 16299.15, you can clean install or leave the Insider Program without worry of your install eventually expiring under the Insider Preview. This is the official, non-preview release of the Fall Creators Update.