What was your source of the 515 software ?. I drew a blank looking at the Spanish thread although I might have missed a link.
I noticed a few sharks in play in this thread in places claiming that they had the trusted source and others didn't. Presumably the software has a signed SLA1 metainfo txt file like the navigation high updates which prohibit meddling with the source since you can't generate the signature yourself. That's the argument deployed plus if you dont use ODIS it can get reset, but then I recall RCupra said you can only upgrade firmware, not downgrade, so that doesn't stand up.
Is it anymore reliable?. Suppose to fix Android Auto and Carplay bugs.
Did you need VCDS / Obdeleven etc to finish it off or just plug & play... Do you want to right a resource.