Microsoft has today pushed a new Fall Creators update preview build for insiders in Fast Ring. The Build 16299.15 is now available and can be installed. The build comes at a time when Microsoft is looking forward to intensifying the final round of testing for Fall Creators update.
This is the minor update over the last Build 16299. Microsoft seeks to establish this build with a cumulative update so it seems that it is the RTM Build.
UPDATE 10/2: We have released Windows 10 Insider Preview Build 16299.15 to Windows Insiders in the Fast ring. As we prepare to release the Windows 10 Fall Creators Update to the world on October 17th, we will now start testing out servicing this build with the Cumulative Updates via Windows Update.