Saw this post. Another '15 GTI here, original owner. Mine is peeling pretty good as well. Took it by the dealer today to see if there was anything they could do. They took photos and sent up a claim. Will share what I hear back. Expectations aren't too high but I figure if enough '15 owners are reporting up the same issue, maybe they will acknowledge it
Can confirm it isn't adhesive underneath as it flakes off, it started in the front as shown in the photos but is also peeling at the back edges now as well. Car is very regularly washed and waxed despite being dirty in the pics lol so ultimately sealant didn't stop it. Took one part to flake off and it went fast after that. It has spent mixed time indoors and garaged. Cali and Hawaii sun probably added to it