I just did the image download and apt-get from the Raspi script today so the kernel I have matches what you listed above: 4.19.93-V7
Are there docs for V15 for install and config? I am not sure what AX.25-Control does on the desktop. It runs a while and then stops. I do a pidof direwolf and don't see it running either before or after running AX.25-control.
I know that the V14 docs really don't apply to V15.