Stand if the dealer has an upcard of 2 through 6.
Otherwise take a hit.
A hard 13, 14, 15, or 16 isn't a great hand since the chance of going bust is pretty good. Lots of cards can hurt you, which is why these are called "stiff hands".
If the dealer has a 2 through 6 though, she has a good chance of going bust, so you're better off just standing and crossing your fingers.
If the dealer has a 7 or better though, chances are good that the downcard is a 10. And if that's the case, the dealer will stand and won't possibly bust. So you need to improve your hand in order to have a chance at winning.