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 [0].

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 [1]. The
Fedora Project wiki also contains instructions [2] on how to upgrade
from a previous release of Fedora to a version receiving updates.

Cheers,
Robyn

[0] http://lists.fedoraproject.org/pipermail/announce/2012-May/003078.html
[1] https://fedoraproject.org/wiki/Fedora_Release_Life_Cycle#Maintenance_Schedule
[2] http://fedoraproject.org/wiki/DistributionUpgrades