As of 26 June 2012, Fedora 15 has reached its end of life for
updates and support. No further updates, including security updates,
will be available for Fedora 15. A previous reminder was sent on
May 31st .
Fedora 16 will continue to receive updates until approximately one
month after the release of Fedora 18. The maintenance schedule of
Fedora releases is documented on the Fedora Project wiki . The
Fedora Project wiki also contains instructions  on how to upgrade
from a previous release of Fedora to a version receiving updates.