I would expect stock wheels with 295/70/17 (which is essentially 33x11.5) would rub when you turn unless you add spacers or washers on your steering stops. Washers on your steering stops is cheap and easy (see here
), so, technically, I think you could do this for at least on road driving.
Offroad, the tires are fairly likely (though not guaranteed) to rub your fenders when flexing the axles, and for that you'd need flat flares or a lift. DIY flat flares are cheap and sort of easy (see here
) and a basic budget boost doesn't cost too much, so, again, you could technically have no real problems here.
That said, as indicated by Vacca above, make sure you price check (New 15" Alloy Wheels + 33x12.5R15 Tires - Money from selling stock wheels/tires) versus (New Nitto Terra Grapplers for 17" wheels). Depending on how good of deal you're getting on the Nittos, you may be surprised. Getting the new wheels would, as a bonus, mean that you don't need spacers or steering stops to stop the rubbing on turns.
To get a sense of the ballpark prices, send a PM to forum vendor Discount Tire Direct for some quotes on a good 15" wheel and 33" tire set up. Then spend some time on eBay and your local Craigslist to get a sense of what you could resell your current wheels/tires for.