Microsoft has released Windows 10 Mobile Insider Preview build 15245 to the Slow ring. The build replaces 15240 in the ring, which was offered on August 24.
And just like with 15240, the company didn't tell anyone that there's a new Slow ring. There are no tweets about it on Insider chief Dona Sarkar's or the Windows Insider Twitter account, and the original Fast ring blog post for 15245 hasn't been updated with any new information.
Sadly, ignoring Windows 10 Mobile seems to be more and more common with the Insider Program. Microsoft has even released Mobile builds to the Fast ring on days where it was promised that there would be no builds. Simply put, Windows 10 Mobile just doesn't seem to count anymore.
Build 15245 doesn't add any new features when coming from 15240. It really just focuses on fixes, as do the vast majority of builds from the feature2 branch. The latest Fast ring build, 15250, has doubled the amount of new features coming in the update though, to a grand total of six.