It has probably turned rancid. And, yes, fifteen years is too long to store any food in the freezer.
A cooking method tells you how much to put of a certain ingredient, how to cook the food, and how long to cook the food for.
how long can cut sweet potatoes stay in water before cooking
This food will keep for about 5 days in the refrigerator. Place the food in an air tight container for the best results. This food can easily be transferred to the freezer for longer storage time.
5000000 years
it depends on what your cooking
you didn't say how you were cooking it or what colour it turned that you consider it discoloured. As for it softening, that is the whole point of cooking it,of course if you cook it too long it will go mushy
as long as u want
The cooking term, chill, means to set a food in the refrigerator long enough to allow it to become cold.
Yes.
it depends on the food you put into the foil
No it needs to be frozen if not used on a couple of days