I have signed and pushed the libvirt-1.2.15-3 and kenel-3.18.12-11 RPMs into the xen4 repository for CentOS-6.6. These have been in virt6-testing for a few months now with no negative reports.
They should be available on mirror.centos.org in 30 or so minutes and externally as those mirrors update themselves against mirror.
Thanks, Johnny Hughes