There you have it… “simply unpacking binaries to a dir is not a good way to update the package” and for 1.15.0 I can promise that won’t do it… the official way to install/update pkg on FreeBSD is using pkgng or the ports system.
The port it self is not updated yet to handle this, possibly because this is still beta, and they will only do it when it goes public.
If you want to do it using the ports system, it might help to look here: Plex server doesn't work after update
I posted a Makefile and rc.d diffs that should help (but you must understand how that works, if that’s not the case it might be best to wait for them - freebsd maintainer - to update the port)
