A few things
Rugby is a great sport, I played it for many years during school and loved every minute. Back then I had the same problem as you, I was pretty small. I spent my summer “bulking” following bad advice from internet forums. Now, older and (hopefully) a bit wiser, I realise that this wasn’t the best thing to do.
Rugby is a sport as much about speed as bulk. Yes you need to be big but if you are big and slow you will not reach your full potential. So that said;
Start eating more healthy food. Stay away from fast food joints and focus on eating plenty of nuts, eggs and lean meat, and drinking plenty of milk.
Your workout time at the gym seems a bit excessive, I would suggest replacing some of that time with cardio, interval sprinting specifically. In the gym focus on the traditional mass builders, squats, deadlifts and bench pressing. To give you that extra snap in a scrum mix it up with some Olympic lifts, snatches and cleans.
Whey protein shakes will definitely be helpful, I would also recommend trying some quality casein protein shakes if you have the cash. I wouldn’t recommend, in fact I would strongly deter you from using creatine supplements for now. It’s your choice but I don’t think its necessary for an athlete of your age, or any age for that matter, I’m sure some people will have different opinions to me.
I couldn’t really predict how much weight you could put on but using the above methods should definitely add a fair bit of muscle, and minimize fat gains.
Good luck in your training and your games.
PS: my blog
Real Strength Training contains information that is probably a bit basic for you but I will soon be putting up sport specific articles, including one on rugby