Normally F15 getting a new kernel would mean I would be produce and announce new updated Livecds.
But sadly today is not the case due to a bug that has been introduce sine the last updated livecds (20110823)
https://bugzilla.redhat.com/show_bug.cgi?id=734993 is the bug i am referring to
I will help watching and when this issue is resolved I will gladly produce updated livecd.iso
The 20110823 isos are still available http://jbwillia.fedorapeople.org