http://wccftech.com/windows-10-fall-creators-update-cumulative-update/

With Windows 10 Fall Creators Update making a public debut next week, the company has sent a second cumulative update to Insiders currently testing the build 16299.15. Following the release of the RTM build 16299, Microsoft had rolled out a cumulative build 16299.15 earlier this month. The new cumulative update brings the build number up to 16299.19.

Please note that is not a new release but a cumulative update intended to bring some fixes ahead of the Windows 10 Fall Creators Update’s public release. “This update only includes quality improvements and no new OS features,” Microsoft wrote in its announcement post.