The USA is a big country to traverse, you will find a 15 day plan woefully short, and a months plan ideal. Though there is something for everyone, it would make sense to travel by bus if you are on a shoe string budget, bus rides are great and give a sense of the scenery. Airplanes are, if you are short of time as you would be on a 15 day trip while on a longer trail time, you could have a mixture of bus, train and aeroplane travel.
5 ways to enjoy USA :
1. Plan plan plan in advance.
2. Plan for 4 days at Washington DC, the museums are overwhelmingly good.
3. 2 days at New York.
4. If you don't have time, take one coast at a time, say East and do the West coast the next time.
5. Stay with a relative if possible, make that location your home base.
The USA is a great place to be, enjoy it in all its totality.
