4 year degree is an officer, you can sometimes collect a pension at 15 years. If the military is downsizing, and are forcing you out at 15 years, sometimes they will offer a partial retirement or a lump sum severance package.
IF you're in a high demand MOS you WILL NOT be switching jobs unless you're medically incapable of doing your present MOS. Even then they usually just stick you in an office doing paperwork for your original MOS.
You should join as an 0311, only job in the marine corps (just like corpsmen are the only real men in the marine corps, says it in the name

)