If I read the OP, the SUV is 5k upside down, and this is a 15 year loan. You are plopping $6000 down.
First, I wonder about selling the SUV separately at the cost of the loan, and paying the difference so you are out from under it. This will make life a tad simpler.
Second, after jettisoning the SUV, can you wait a bit and go for a bigger down payment? This way, you can either keep the 15 year term and go for lower payments, or go for 10 years and have the interest rate cut down by a good amount.
I am almost exactly in the OP's shoes. I am looking to buy a class "B" motorhome, and -can- buy one now. However, since I have no vacation time coming up for a while, and the "B" market is going through a lot of changes due to the new vans, I'm biding my time. I want to have my existing rig either completely paid off or to the point where I can sell it for 75% of NADA low and walk away. This way, at -worst- the rig gives me $0, and isn't a further expense.
I also am biding my time because I want to have at least 20% down. For a rig like the OP's, I'd like to have $14k on the table. This is because the economy is uncertain, and if I lose my job, I can fire-sale the RV for a fraction of what it is worth and walk away.
However, everyone is different, and it might be better to start trips and enjoying the open road sooner rather than later.