Without knowing the specifics of the mortgage and any refi costs, it's hard to say, but here's the back of the envelope math:
-For every 1% in lower interest on every $100k of mortgage owed, you'd save approx $1k a year.
-Supposing you had $3k in closing costs, and a $150k mortgage, lowering it by 1%...you'd be saving $1.5k a year, and you'd break even after 2 years.
-Unless you're moving fairly soon, or unless you're paying your mortgage off very soon, I'd say it's time to refi....but you'll have to run the numbers to be sure.