Current Branch 1511 is now out of support
Just in the event that you were not aware, as of today (12/8), the original release of Configuration Manager current branch is no longer supported. Each release has a one year support cycle, after which time you are no longer within product support. That does not mean that it stops working at all, just no longer supported.
Of course, there is no reason to still be on 1511, as it is so easy to update to new releases when they come out with the Updates and Servicing feature.
1602 is still supported, and certainly 1606 and the newly released 1610 (most of you probably have seen the download for it in your sites by now, they slowly release it to different 'rings' over a couple weeks timeframe).
Good luck all, let us know if you have any questions on it.