[twobob]

No, that value after the colon is the Display reference number (as hawhill says) so you said "Display 22". you must have meant "port 22" thinking of ssh?

Generally VNC by convention is Port 5900 + XDisplaynumber, That is the default TCP Port on which the VNC service listens IIRC.

:1 or :0 would be the most likely, actual, display numbers....

Punch open your ports 5901 and 5900 for good measure.

iptables -I INPUT -p tcp --dport 5900 -j ACCEPT
iptables -I INPUT -p tcp --dport 5901 -j ACCEPT
(or w/e system you use to lock out ports)

Connect to 192.168.15.1:0 or 192.168.15.1:1 ?

I'm only guessing as I don't know your network nor your hardware.

Also as hawhill said, install KTERM and run the program in a terminal via the backend's command line interface for more meaningful errors.