Our average rehab is $4,000 ($2,000 parts and $2,000 labor) and an extreme one is $10,000 (that's a home that is a total wreck). $15,000 is way too much. If you drop that number to $10,000, then there are more questions that need answered:
1) Is this a very visible spot in the park that needs dressing up, such as at the entrance of a "curve in the road head on" shot? That would make the new home increase the overall value of the park, and it's not all about the price of the home.
2) Does the CASH program work in your park? Don't just assume it will, because it often does not. It's based on bunch of variables that you don't know until you test it.
Personally, I'd hold off on rehabbing the interior of that home, but just do the exterior for less than $1,000 and moth-ball it. If you want to test CASH, bring it into a vacant lot so there's no immediate decision to make. If it works, and the spot is highly visible, then maybe put a CASH home on it. If not, then see if you can sell that home as a "handyman special". Traditionally, you should devote your CASH homes to filling vacant lots -- that's where all the money is. Most any POH can be brought back to life for $10,000 and under, and it's typically the better choice unless it's a highly visible spot. In the absence of CASH, a new home will cost you more than $10,000 out of pocket, and you'll be better off doing the rehab.
And I'm not even including the risk or having the city fight you on bringing in a new home vs. fixing the old home, or the site preparation costs in your state (if you're talking Nebraska, swapping the old home for the new one will cost you around $5,000+ in site preparation).
As you can see, it's a complicated question.