If you want the hassle-free method, just use the version from Oracle's website,. Setup their repository by copying it to /etc/yum.repos.d/, install kernel-devel and dkms (!!), restart, install VirtualBox-5.0 (sudo dnf install VirtualBox-5.0). I am doing that this way since Fedora 18 and never had a single problem with VirtualBox. Yes, it's not a free GNU piece of Software like kvm/qemu implemented in Boxes but it also works just fine.