Insiders are receiving a second set of Insider builds in the Fast ring for PC and a new Mobile build too.
Microsoft is rolling out a second set of Insider Preview builds this week, with build 16275 for PC and 15245 for Mobile now rolling out for Insiders in the Fast ring!
Build 16275 for PC is only available for Insiders in the Fast ring who did not choose to Skip ahead. Skip ahead users will be getting a newer build next week.
Full story from the WindowsCentral blog...