There is a term called "steroid responders". These are people in which use of steroid eye drops results in sudden and alarming rise in there IOP. In such patients using steroids for 15-20 days as you mentioned can cause glaucomatous damage. If you are not a steroid responder then it has been seen that the IOP rise is not necessary and high enough to cause significant damage in 15-20 days. Still one should keep a check and get IOP measurement done. Also you should taper the steroids when you want to stop them and not just stop them at once.