The lie of your Irons can be bent by 2 degrees upright or flat. Find a fitter with a loft and lie machine who will be able to do it for you. You don't need to buy a new set, unless you're looking for an excuse to buy new irons.

You can have cast clubs bent slightly, up to 2 degrees but you should have Titleist do them or you risk voiding the warranty. If they are already out of warranty, make sure the place you go will guarantee their work if the happen to snap one off. The real question is, are they too flat for your current swing? Unless you have dramatically raised your hand position, its pretty unlikely that your lie angle has changed unless it was a bad fitting to begin with. Lie wouldn't really impact height of your shots. Typically a club too flat would push or slice and a club too upright would pull or hook. Low trajectory from your irons is usually an indication that you are de-lofting by getting the shaft too far forward at impact or casting and catching the ball on the upswing without creating enough backspin. Getting fit for a new set might not be too bad an idea. Go to the fitting asking to maximize your iron flight and they will help you get a shaft that will give you the best results possible. The rest is lessons and hard work. Good luck.