We run all our non-physical FreePBX instances on Hyper-V - They work great and have for years.
There is a (pain-in-the-you-know-what) way of upgrading a 13-Instance that is already in Hyper-V and it involves copying the VM into VirtualBox - once you have it running in VB, you can upgrade it to 14 (and probably 15 if you want) and then shove it back into Hyper-V because VirtualBox will mount and use a .vhd - but I would not even bother unless it was a VERY complicated setup - you will be happier with a scratch-load of the version you are looking for.
Here is the original recipe: