It is really important having the chance to run MongoDB on Windows Server 2012 R2, as it looks like Windows Server 2012 and the previous versions have the 8TB memory limits for the virtual address space:

From Wikipedia - http://en.wikipedia.org/wiki/X86-64

Prior to Windows 8.1/Windows Server 2012 R2, Windows for x64 offered:

8 TB of virtual address space per process, accessible from both user mode and kernel mode, referred to as the user mode address space. An x64 program can use all of this, subject to backing store limits on the system, and provided it is linked with the "large address aware" option.[69] This is a 4096-fold increase over the default 2 GB user-mode virtual address space offered by 32-bit Windows.

8 TB of kernel mode virtual address space for the operating system. As with the user mode address space, this is a 4096-fold increase over 32-bit Windows versions. The increased space primarily benefits the file system cache and kernel mode "heaps" (non-paged pool and paged pool). Windows only uses a total of 16 TB out of the 256 TB implemented by the processors because early AMD64 processors lacked a CMPXCHG16B instruction.

And also from the Windows documentation - https://msdn.microsoft.com/en-us/library/windows/desktop/aa366778(v=vs.85).aspx