Convert a template designed and tested on v1.3.9 to v1.5 ?

Is converting a template designed and tested on Zen Cart v1.3.9 to v1.5 possible?

I have a template I purchased from Template Monster and it has NOT been updated. I contacted Template Monster and they said the designer who made the template is no longer with them. So I'm basically SOL.

Hope someone out there Can please me?! I can provide files/code need upon request.

Thanks in advance!

It really depends on how correct the initial implementation was in the first place. If the TM person did what TM "designers" usually do, then they probably hacked it all apart and made a mess ... and thus converting it to any other version will not be as straightforward as it would be for most templates.

With a properly built template, upgrading it is just the same as upgrading any Zen Cart site: compare the old version's template against the original old version code, and then rebuild those customizations into the new template using the new version's code.
Comparing the two sets of original Zen Cart files with each other will also help you see what specific changes were made in template files between the versions, and help you know what changes need to be incorporated in your custom template.
Either or both approaches may be helpful in getting you to your desired end result.

Have you tried seeing if your TM template works with 1.5? Perhaps you can pop-up a test 1.5 site and see.