Microsoft were originally planning to release the first Insider Preview build of 2017 this week, but after looking at feedback from internal flight data, decided against doing so as the build candidate they had lined up, according to Microsoft, has issues with updating build-over-build. Build 15002 was the build in question, and has now leaked out as a WIM image.
The WIM comes directly from Microsoft's own servers (thanks h0x0d for spotting it), but has since been pulled. The WIM was re-uploaded elsewhere, so if you're interested you can still give it at download. We don't recommend doing so however, as a WIM image is a little harder to work with over your standard ISO file as it needs to be converted, among other things.
Not only that, but Microsoft outlined why they didn't release this build earlier today, citing update issues. Installing this build may cause instabilities when updating to newer builds, so it may be best to stay on build 14986 for now.
Build 15002 includes most of the changes found in the recently leaked build 14997, so we're not expecting to see anything we haven't already seen in this build. Stay tuned to Windows Central for more coverage on builds and the Insider Preview!