Earlier today, Dona Sarkar noted that Insiders will be going yet another week without a Fast ring build, as there now hasn't been one in 30 days. The reasoning for the delay was posted to the Feedback Hub, citing an issue with N+1 updates, meaning the process of upgrading a build to a newer one.
It would appear that that build was to be number 15002, as it's now been leaked online. Twitter user and renowned Microsoft leakster WalkingCat spotted it under Desktop App Converter base images.
As with all leaked builds, you're installing it at your own risk. In fact, there are a couple good reasons why you shouldn't, one being that this is a Desktop App Converter Base image, rather than a standard ISO installation image.
Another is the reason that Dona cited for the delay. N+1 means that you might have trouble getting future builds, and keep in mind that the last build, 14986, was the first to use Microsoft's new Unified Update Platform (UUP). The build to come after is to be the one where users will actually experience this, so it seems likely that UUP is responsible for the issues that the team was facing today with 15002.
Also, we don't even know what, if anything, has been added to this build since 14997 was leaked two weeks ago. Perhaps it might be best to sit this one out and just wait until there's an actual Fast ring build next week.