I'd say a majority of that stuff is crap, what you need is just a better source of calories from real food.
There is a while section devoted to nutrition on this site. I suggest you start with the basics like counting calories and eating a lot more/more healthy.
Eating to gain weight is a pretty large commitment and takes a great deal of time to really understand.
Since your at such a young age you don't have much control of the food your parents buy but I'll bet you can at least start making smarter decisions.
To tell you a little story, when i was your age i was eating Marie Callinders pot pies twice a day and sitting on my ass.
I later learned that those same pot pies have an insane amount of bad calories and have recently been dubbed the worst packaged food in America.
I also got fat that summer, don't make the same mistake i did.
Now i'm not expecting you to strict diet at your age.. mainly because your 15, but if you really want to get bigger (in a healthy way), you have to start changing some of your habits.
Finally, if your really looking to supplement in some more calories, you can go buy some protein powder from the GNC (I use the brand called ON whey 100%, and it tastes pretty good).
I realize you can't really control the food your parents buy so this might be an easier change than choking down that other stuff.