Hi James,
Yes, you can simply copy the VMs over.
We aim to maintain VM compatibility across product versions to the highest degree possible. We don't always get that compatibility 100% right, but we would generally expect that a Windows guest with a reasonably "normal" configuration, migrating from Player 5 (from 2012) to the latest Workstation Player 15.5, should not encounter any specific issues. The VM's file formats are all compatible across that range of versions.
Regarding optimizing the VMs for the migration:
If your new host has a different CPU or GPU model, there is some risk in moving a suspended virtual machine (which is effectively "still running") from one host to another. Again, we try to keep that compatibility as close to 100% as we can, but sometimes it is simply not possible – particularly when CPU vendors start removing features from their newer CPUs! If your VMs are suspended, I would advise resuming the VMs on the old host (if possible) and shutting them down normally before copying it over. If a snapshot is copied, Workstation Player might warn you about changed CPU capabilities when you try to resume the VM on the new host, and the guest OS might potentially crash if you continue anyway.
When you start using the VM on the new host, Workstation Player will probably ask whether the VM was moved or copied. If you do not plan to power on the VMs anymore on the old host, choose "Moved", even if you actually copied them. Choosing "Moved" will ensure that your virtual machine's network identity (MAC address) is kept unchanged; Choosing "Copied" will generate a new MAC address – which would allow the "source" and "destination" VMs to coexist on the same network without interfering with each other.
Be aware that you might need to re-activate the Windows guest OS if it feels that too much hardware has changed. If there is a change of CPU, the guest OS will be able to see that. I don't recall precisely how fussy Windows 7 is with its product activation. Likewise for other software installed in the VM: There is a chance that applications could see that the hardware has changed and demand that you reactivate/relicense to keep using it.
Finally, keep in mind that Windows 7 is out of support, and Microsoft has made clear that they will not necessarily be supporting Windows 7 on the latest CPUs, so there might be some inherent risk in running Windows 7 on a very new host. Be very careful about connecting a Windows 7 guest to a network, since vulnerabilities in its software might not be receiving fixes anymore.
Hope this helps!
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Darius