schedule: 1.15 is now out of support
schedule: 1.15 is now out of support

As of the 1.15.12 release we are no longer backporting patches to the
release-1.15 branch.

Signed-off-by: Tim Pepper <4807564e5a18784afafcf20dbdb5591e844b9075@vmware.com>

kubernetes/sig-release