We cannot shut down the 4.15 pipeline, because we have to allow 4.14->4.16.

Options at hand:

1. Stay with broken 4.13, 4.15 - not many customers are there
2. Release 4.13, 4.15 manually every 8/12 weeks
3. Automate 4.13 4.15 slow release
4. Enable direct 4.12->4.14/ 4.14->4.16/ 4.16->418 upgrade path