I'm going to cook a 15 lbs. turkey in foil. This is the first time in 10 years I have cook a turkey so I let it thaw in the refrigerator for 72 hours. Rinse it and tin fold it all over and pre heat the oven at 450 and cook for 3 hours?
You're doing fine, LS, though I am surprised that you found this somewhat unconventional method rather than the more usual ones mentioned above. Did it come out of a Google search?
The kid and I used this method two Xmases ago, after she read about it on a university site, I think. At this high temp, escaping moisture cannot condense on the inside of the foil and so the bird is braised rather than roasted which is fine unless you are looking for crispy skin. I think that she wanted to avoid having her mom eat too much "unhealthy" skin!
A cuppla tips. We brined the bird first, though I doubt that that would affect cooking time or method.
We wrapped the bird in 18" wide, heavy duty aluminum foil and placed it in a roasting pan. You can either stuff it -- if so, check the stuffing's temp when you pull out the bird -- or fill it with diced onions or some other aromatic veg, which is removed after cooking and serve with a separately prepared dressing.
Stick a thermometer through the foil and into the center of the thigh to monitor the temp. It will cook in under 3 hours but not a lot. Use the internal temp as your guide.
If you wrap the bird too tightly in foil, the steam pressure will burst the wrapping open, of course. We cut a couple of small slits on top with scissors.
Obviously you need a preheated oven, but this method obviates the need to pay the bird much attention while it is cooking. Just take care to start checking that temp after about 2 1/4 hours.
Cheers