Although frequently (not always) a 15 year loan will have a slightly lower rate than a 30 year loan. Less risk to the bank.

The advantage to paying off a 30 yr loan as if it was a 15 yr loan is the flexibility of payments versus being locked into a 15yr loan and then trying to get a 30yr loan when you can't hack the required payments.

For example, 300k loan @ 5.75% (ball park current rates) for 30yrs
Required payment (P&I only) is 1751$
Adding 750$ in principal payments will pay the loan off in 15 yrs, resulting in a savings of 182k in interest payments as compared to the 30 yr loan.

You should get a slightly lower interest rate for a 15 yr loan
For example, 300k loan @ 5.5 (Again, ballpark rates for 15 yrs)
Required payment 2450$

Comparing the the 30 vs 15 year loan
30 yr interest payments =330k
15 yr interest payments =141k
30 yr paid off in 15 gets you interest payments 148k

So, to save 7k (500$ a year), you are locked into that higher payment for the duration.

But, back to whether you should buy the house or not. If you qual'd for a 15 yr loan on your dream house, then a 30 yr should be a no brainer. And while I don't know your situation, I would think going from a WB Capt to a NB Capt, or a NB Capt to a WB FO shouldn't push you that far over the ledge. If nothing else, minimizing your contributions to the 401k&IRA should be able to tide you over for a few years.

What you should do is sit down with CinCHaus, and flip a coin. Heads you buy, Tails you don't. Catch it in midair, and try and figure out what you were really hoping it landed as.

Caveat, if you just bought 2 new Cadillac Escalades w/ no $$ down, maxed out credit cards, just say no. And get your house in order, contract is only 2 yrs away. Not too early to start building up the bank to ride out any contract shenanigans