What a coincidence, someone was doing same, same versions, last week in this thread
Ah, it was you 
It's not really considered good etiquette to open parallel threads on essentially the same topic.
Good decision. You were told 8.15.x was ages old on the other thread.
The other thread stalled when it was suggested you do the same 7.x --> 8.x upgrade on a throwaway environment first. You wrote:
"It is hard to get another environment for trial/testing purposes"
I am glad you have solved this issue and are able to deploy a completely different parallel cluster!
Anyways, I agree with @leandrojmp and @DavidTurner - in your situation I think you have better chances with an upgrade which, IMhO, is significantly simpler and is likely safer too.