Hello,
On my system, the boot phase takes only approximately 28 seconds but
both the reboot and shutdown phase take approximately 1 minute and 10
seconds.
This did not happen with F16.
I think this is not normal. In my case, F16 spend less than half time
shutting down than F15 in the same computer. You can try enabling the
log display to see what is spending so much time. This can be done
editing grub2.conf and removing rhgb quiet params.
Emilio.