Q. What is System Center Configuration Manager 1511?
A. System Center Configuration Manager 1511 marks the first release of the new path for Configuration Manager as a Service type solution that will constantly be updated with monthly updates instead of major new versions every couple of years. The new naming of releases reflects the year and month which means 1511 is 2015 and the month of November. A future release could be 1603 which would reflect 2016 and March. This was announced at http://blogs.technet.com/b/configmgrteam/archive/2015/12/08/system-center-configuration-manager-ga.aspx. The need for a faster cadence of Configuration Manager updates is partly because of the new release cadence of branches for Windows clients but also because Configuration Manager now supports management of mobile devices which means Configuration Manager has to be updated at the same pace as the operating systems it supports.
1511 can be downloaded and existing Configuration Manager 2012 SP1 and R2 and above deployments upgraded fairly simply using an in-place method. Information on the upgrade and requirements can be found at https://technet.microsoft.com/library/mt627853.aspx.
Future updates will be simple to deploy from within the Configuration Manager console itself. This will be available via the Administrative workspace via Cloud Services - Updates and Servicing. You will be notified of the components being updated and there will be the ability to delay application of updated branches for a period of time and note that the updates will be cumulative.