Let's have a look at current situation first. The existing server is build on Windows Server 2008 R2, SQL Server 2008 R2 and ConfigMgr 2012 R2, where the Primary server installation is separated from SQL installation. You may upgrade SQL Server in-place with Microsoft support, but an in-place Windows Server upgrade is not supported. Therefore a new server with a current (2012 R2) server installation is needed. When using Windows Server 2012 an in-place upgrade to 2012 R2 is supported. Otherwise not!
When building a new server, and there's a need to use the existing ConfigMgr database, the computername, IP-address and partitions must be same. Because I want to change the name and partition both, recovery is not possible. Therefore I used a new server build on Windows Server 2012 R2, SQL Server 2014 SP1 and and ConfigMgr 1511. During installation a new Site code and name is requested. The existing name cannot be re-used.
After installation start the migration tools, and migrate all objects needed to the new server.
All went fine during this migration. Hope it helps!
Update 28-12-2015: Within the Object migration task, collections can be selected as well. As asked by Conor O'Farrell within the comments, both deployments and collections can be migrated successfully. On my software package however the program was disabled after migration, without the possibility to enable it during migration. So yes, you can migrate all stuff needed from ConfigMgr 2012 R2 to 1511. Just great!
Backup and Recovery in Configuration Manager
How to move the ConfigMgr 2012 site database to a new SQL server
Supported configurations for System Center Configuration Manager
Planning a Migration Job Strategy in System Center 2012 Configuration Manager