Just some numbers on the scenario you laid out assuming you have a full 30yrs left on a 60k loan @ 5.5% VS. a 4.25% 15yr loan.
You will pay $62,642 in interest on the 30yr loan VS. $21,246 of interest on the 15yr loan. A savings of $41,396......the payment on the 15yr loan is $110 more per month.
All true statements about importance of the costs of your refinance as well as how long you plan to hold this mortgage.
I am simplifying a bit by ignoring tax benefits but if the time you plan to stay in the house well exceeds your breakeven point it makes sense to refinance.
1) How much are your closing costs?
2) How many years do you already have invested in your current mortgage?
If you've had your current loan for a while, it may make more sense for you to pay extra each month towards the principle of your loan.
Just for the sake of argument: On a $60,000 loan at 5.5%, the monthly principle an interest payment should be $340.67. If you add an extra $150.00 per month, the loan would be paid of in 15 years.