The 15.4 kernel failure needs to be reported as a bug:
https://en.opensuse.org/openSUSE:Submitting_bug_reports
https://en.opensuse.org/openSUSE:Bug_reporting_FAQ
https://en.opensuse.org/openSUSE:Bugreport_kernel
When you make your report, be sure to mention, and provide the URI to, this thread. With any luck, a fixed 15.4 kernel will be made available before you need VBox working.