Whew. If you have basic electrical skills or know someone who does, you can..
Replace the plugs on the wires you have.
Chase down where the two wires go and what they power.
Decide what to do.
I personally would be concerned about your wiring till you can figure it out. On the other hand, If everything has worked well in the past, just get a 50 to 30 amp converter and see what happens. Plug in the 30 amp plug and see what works and what doesn't. What doesn't will be the circuit that the 15 amp plug powers.
2007 Chevy 2500HD Classic LBZ Duramax/Allison (Stock)
2005 Bigfoot 1500C8.2 AWESOME