Can I migrate a CM 2012 site to a CM Current Branch site?
Is it possible to use the Configuration Manager migration feature to migrate objects from a Configuration Manager 2012 site to a Configuration Manager Current Branch site?
In the past, the migration feature of CM has required that (unless you were migrating from CM 2007) that the source and target be the same version of CM 2012. Reference here https://technet.microsoft.com/en-us/library/gg682006.aspx "Beginning with System Center 2012 Configuration Manager SP1.....migrate from System Center 2012 Configuration Manager infrastructure to another deployment of Configuration Manager that runs the same version."
Suppose you are currently running CM 2012 and want to build a new parallel hierarchy to run CM CB and then migrate objects over. This may be a common scenario due to OS requirements for CM CB (Server 2012 or later) and SQL 2012 (or later). Now, CB 1602 will allow you to perform an inplace OS upgrade (say from Server 2008 to Server 2012) but most customer aren't comfortable with upgrading a server OS, they would rather start with a fresh install. So, if the prior migration guidance still applies, you would have to either:
- upgrade source CM 2012 to CM CB, install target CM CB site, then migrate
- keep source site at CM 2012, install CM 2012 on target site, migrate and then upgrade target site to CB.
Those aren't bad solutions, just has some extra steps that would be nice to avoid. Luckily, CM CB supports migration from a CM 2012 source site. Reference https://technet.microsoft.com/en-us/library/mt593351.aspx#BKMK_SupportedMigrationVersions 
"You can migrate data from a source hierarchy that runs any of the following versions of Configuration Manager:
- Configuration Manager 2007 SP2
- System Center 2012 Configuration Manager SP2 or System Center 2012 R2 Configuration Manager SP1
- A System Center Configuration Manager hierarchy of the same or lesser version of System Center Configuration Manager"
That's great news. I've tested this in my lab and seems to work on CB 1511 when I migrated from a CM 2012 R2 SP1 site. Monitor the migmctrl.log and you will see lots of Query against Legacy Site messages. I hope you find this helpful