If you will get a much lower rate than you are currently paying, refinancing makes sense. Make sure to factor in closing costs to get your break even point on the refinance. If the break even analysis shows it doesn't make sense to refinance, just pay extra each month on your 30 year as if you would pay it off in 15 yrs. Some would suggest investing the additional funds and keeping the 30 yr, but that doesn't factor risk into the equation. My recommendation would be to make payments to pay off the house in 15 yrs and then invest anything left over after that.