This thread has now been closed to direct all further updates about this release onto the latest announcement:
Please see https://releases.xamarin.com/beta-release-15-1-rc2/ for the details about this release, including the steps to update or downgrade as needed.
This release uses a new naming convention "15.1" that more closely resembles the sub-version numbering of Visual Studio 2017. "15.1" in this new scheme matches up with what Xamarin would have called "Cycle 10" under the old scheme.
This release is now available in the Xamarin updater channels and as part of the March 27 update for Visual Studio Preview. Note that the Xamarin version number in Visual Studio 2015 is slightly ahead of the version number in Visual Studio Preview in order to provide early availability of a few additional fixes. Xamarin coordination with the upstream schedule has been evolving across the VS 2017 releases, and plans are underway to synchronize more tightly as soon as possible. Watch for additional news on that topic as the 15.1 release moves into the Stable channel in the upcoming weeks.
Please file a quick bug report using the current "Feature Preview" new bug form if you see any suspicious behavior in these versions that you wish to report.
Comment in this forum thread if your question is not related to a suspicious behavior after download, but instead one of the following:
EDIT Mar 27: Update link to Release Blog post for new versions. Add information about Visual Studio Preview.