Yes it has been merged, however given that the merge window only opened recently the 3.15 release will be 3-4 months away. Given that time frame its not likely that 3.15 will make it into the autumns Linux distribution releases. Probably be a year before this gets into the hands of users.
(unless someone backports it or you build your own kernel)
Suse tumbleweed, the Kernel Developers PPA, Debian Experimental / Unstable, Arch, Fedora Rawhide, and Gentoo all deliver new kernels usually within a month of release, most within days (albeit more buggy).
I seem to get kernel updates using Debian Unstable (I don't pay much attention; but my current kernel is 3.13 and I installed my current OS years ago) and I think Arch does too. I'm sure there's others.
(unless someone backports it or you build your own kernel)