Got it. Per the usual "don't loan to friends/family", if you're still planning to move forward with it, I would get a lawyer involved in your contract. Make sure that it's not just dead paper that means nothing.

The fact that they can't obtain a small business loan for $15,000 from a bank is concerning. I would look at the $15,000 loan as a gift - you may not get it back.

Edit: how well do you know them? Seems odd that you can't just ask them why they want your DL information.

Sorry, but this. I would expect a rate in the low teens, if you even get approved. I'm assuming you're looking at a long term loan for the RV, as that's the only way it'd be remotely affordable. On a 15 year loan, at 12%, you're looking at a ~$450/mo payment. That would likely push you over 50% DTI. Not to mention you'd pay $40k in interest over the course of the loan.

My suggestion is to resist the impulse to buy, and wait until you're in a better financial position to purchase such a high dollar discretionary item. Sucks to hear, but financially is the best choice.