The 6.1.5 release is built from the same code as the tag
No, it very certainly is not (unless all versions since v.6.0.9 have all been built from the same codebase, which can't be squared with your occasional posts boasting new functionality with each new version). All tags from v.6.0.9 onward point to the same commit: 6e5a84d.
I'm uncertain whether the released .iso files all are built from exactly the same code as is in the corresponding source release .zip file on the releases page. (And I don't think I'd take you at your word if you said they were given how hokey this repo is.) But the tags on that repo at least are 100% pure fiction at best.