Last time I checked, DVC interest rates were:
"Premium" credit with 20% down: 9.99%
"Premium" credit with 10% down: 12.0%
"Preferred" credit with 20% down: 12.0%
"Preferred" credit with 10% down: 14.5%
"Standard" credit with 20% down: 14.5%
"Standard" credit with 10% down: 17.5%
Current DVC member with 20% down: 8.99%
Current DVC member with 10% down: 11.0%
Generally speaking, financing any timeshare is a bad idea. And the longer you finance, the less sense it makes.
There are non-financial reasons to join DVC ("Being a DVC member makes me happy") but, ultimately, the only good reason to buy into DVC is because you intend to vacation at WDW for a long time, can afford to stay at Deluxe Resorts, and are looking to save money. I could number crunch scenarios for you but, seriously, if you buy directly from Disney and are looking to finance over 10 years, it could be decades before you reach the break-even point. (In other words, the point at which you'd actually start saving money.)
Be aware that Disney forecloses on dozens of DVC members every month. With a DVC purchase directly from Disney, it's pretty easy to get in over your head.
If you want to stay at a DVC resort, the best financial advice is to simply rent DVC points through one of the well-known agencies such as David's DVC Rentals. Alternatively, just stay at a Moderate or Value Resort. Heck, for the price on eBay, I like renting a 2-bedroom suite at Wyndham Bonnet Creek, which is essentially on WDW property and can be found for $100/night.
You also could look into DVC resales, which generally are much expensive. For example, Disney's direct price for Saratoga Springs Resort (SSR) is $130/point, while the median resale price for SSR in February was $72/point.
Just trying to offer some friendly advice but if you are looking to finance over 10 or 15 years, I politely suggest DVC is not for you.