I made an effort to compile XEN 4.15.0-rc5 in vmm-xen and succeded at building the packages. (branch is over here GitHub - isodude/qubes-vmm-xen at xen-4.15)
However I get permission denied when trying to start VMs. Anyone tried to compile 4.15 that knows if I’m missing dependencies when upgrading? Maybe I need to also upgrade libvirt?