At 15, I'd say stick with just protein...
I started working out at the same age, and I also tried Creatine, but I think most of my main gains came from just hard training, and good eating (every 3 hours, this is where the protein shakes help save time).
For protein, just get the one with the highest amount of protein per serving. You might also want to take a multi-vitamin. That's all you need, your natural testosterone will give great gains till your mid-late 20's, trust me