For a run of 15 miles each way, stay light. Mine was 21 miles each way.
1. Maybe go once a week by bus to take in clothes, footwear, towel etc. for shower and change. You will need a locker at college and will need to bring in lots of clothes, towels and so on - and take the dirty ones home. Clothing is heavy. Clothing for a week is very heavy.
2. For 15 miles, you might want a couple of fig rolls or similar to boost you if you push hard.
3. I never took a rain cape. I seemed to sweat more inside one than was helpful. However, once it was coldish, i used bib tights and lined, long-sleeved tops.
4. A headband thingy, wooly hat and 'casquette'. If you use a helmet, you may want something warm to cover your ears. If not, the wooly hat when it gets cold and the casquette when warm, clear and sunny.
5. 2 bottle cages: One for water, the other for an old bidon with a 'door' cut into it. In the door put a couple of Allen Keys, levers, a tube or two. Minipump in clip or back pocket.
6. Organise your books and folders. Carry nothing you don't need. You will get good at this very quickly.
7. Mobile 'phone.
8. change for an emergency Mars Bar when you bottom out. It will happen.
That's all I used and it did me very well. Good luck and have fun!