Hopefully you are now playing around with the Windows Server 2016 evaluation version that was released last week (during Microsoft Ignite 2016).
One of the areas that are most fun (IMHO) to test is Hyper-V, there are a gazillion of new Hyper-V features. Anyway, I still have some older Hyper-V hosts running Windows Server 2012 R2, and to be able to export / import VMs from a Windows Server 2016 to a Windows Server 2012 R2 box, they need to be the same version, and Windows Server 2012 R2 really don't get version 8.0 VMs, which is the default version in Windows Server 2016.
Here is a list of supported VM versions:
Supported virtual machine configuration versions
Set the version number
To create Windows Server 2012 R2 compatible VMs, simply use PowerShell and specify the version number. like this:
New-VM -Name "Version-Test" -Version 5.0