I have a passport which expires after 3 years.?
Sure, you can do it while you are in the USA two years from now, but consider these three points: 1) How long will you be without a passport? This could be important in case of an emergency that requires you to travel home or elsewhere outside of the USA. 2) What is the cost of renewing your passport at your country's embassy or consulate (versus what you would pay to renew it at home)? 3) Will it be inconvenient? Does your country require to you appear before a consular official to renew a passport, or can you just send it in with application, photo, and payment? If not, is the university that you will attend close to your country's embassy (Washington DC) or consulate (elsewhere)? Since it is 2015, I assume your country has a website where you could quickly find this information and make your decision.