AirVPN Suite does work fine with Slackware 15.0 RC3 64bit, but I suggest to make the change noted below. I have noticed Intermittent issues with IPv6 on my system with my ISP.
This assumes you are using Network Manager, which is setup via /sbin/netconfig
You should edit file
/etc/NetworkManager/conf.d/00-dhcp-client.conf
and comment out line 'dhcp=dhcpcd' then uncomment line 'dhcp=dhclient'.
Doing that all works fine after a reboot to reset dhcp.
Well spoke too soon, above does work most of the time, but I suspect there is an issue in Slackware with its dbus. Once in a great while IPv6 causes problems with goldcrest (or bluetit or my ISP). I will play around and respond here if I track down the issue.