You're still (usually) allowed to pay back a 30 year mortgage in 15 years by making extra payments against principle. So the total amount of interest paid would be equivalent.
The advantages of getting the 30 yr are
a) You don't have to keep paying that extra principle on your 30 year mortgage. If you lose your job or whatever, you can fall back to making the regular payments
b) The time value of money aspect. My mortgage is currently well below inflation. $151894 in 2035 dollars might be more expensive than $215838 in 2060 dollars. Especially if you're able to reap the tax benefits of mortgage interest.
The advantages of getting the 30 yr are
a) You don't have to keep paying that extra principle on your 30 year mortgage. If you lose your job or whatever, you can fall back to making the regular payments
b) The time value of money aspect. My mortgage is currently well below inflation. $151894 in 2035 dollars might be more expensive than $215838 in 2060 dollars. Especially if you're able to reap the tax benefits of mortgage interest.