I haven't done any specific very old VMware version upgrade to a recent one, but by following what there already is in this Forum, search for "version upgrade", I'm enclosing one link:

https://communities.vmware.com/t5/VMware-Workstation-Player/Upgrade-from-VM-Workstation-Player-5-to-...

There it says that 15.5 should open version 5 VMs. However, if it doesn't, there are other rather recent threads explaining how to change version numbers in the control file to get it running. That is ASCII file editing, where you can try out - I don't have any specific help items for doing this. If not obvious, you could do it by installing intermediate versions, which would allow Upgrade in many steps, according to supported Upgrades between versions. However, that would be time consuming.

As for copying, a simple copy is enough. If you question was somehow about that, here are some points, which may or may not explain, why your open with 15.5 does not work directly:
- I hope you have one VM computer per one folder structure. If you have, then there is no question what needs to be copied

- when copying, you must SHUTDOWN the VM before copying. Especially with recent Windows versions, people do Hibernate or Standby and of course opening the computer somewhere else, after copying in that state, WILL always fail
- if there is some question about media condition or if there is network in play when copying, you must use a reliable copying method. Interactive copy is never a reliable way and often copied VMs will fail when the copying is not good. In Linux, "rsync -urv" is a reliable way. In Windows, it would be "robocopy /e /v /Z" (for convenience, those are not really reliability-related options). Both of those tools work with directories and they have help for many more options, but not really needed in this, in the basic case.

As for something else. Newer VMware softer versions DO require that BIOS has Virtualization enabled. If you don't have it, it will abort immediately. This was NOT the case with older VM software versions, like 12.x. This is also Operating System specific and I'm not sure what Windows 2000 requires. There are also Virtualization parameters in VM itself and it may be that something there is also required (with Win 10 this is so). But I would first turn on virtualization in BIOS and go on from there.