13" or 15" for Computer Science?

I’m going to study Computer Science & Math at NYU and I’m considering purchasing a Mid 2012 15" Macbook Pro. Is the size too big? I like big screens but I’m concerned about portability and the toll it would take on my back. I also create music and use Lightroom and Photoshop for photography and graphic design. Is portability a big trade-off? I use a lot of windows and am used to big screens, and I won’t have a second monitor in my dorm. Should I settle for a 13" inch? I’ve tried it before and it just feels a bit small for me.

15" is not too big. I own a 15" Macbook pro and it can comfortably fit in my backpack and on those small lecture hall deals. Would definitely recommend.