My ONLY concern in doing this would be the effect it would have on the chrome lining in the bore (Assuming yours has it. Olympic Arms generally does not use chrome lined barrels, but their LE rifles may be an exception). In the past there have been reports of people cutting down chrome lined barrels and then the chrome starts to flake off from the cut back. Otherwise, any competent gunsmith could cut down barrel, recrown it, and rethread it.
Personally, I really like and prefer the 14.5" barrel over the 16" barrel. It offer a better degree of compactness, seems to balance much better in my hands, and just handles better, in my opinion.
Previous replies in this thread are greatly exaggerating the effect that an inch and a half of barrel length will have on velocity. I doubt any of them would stand still long enough to let me shoot them with my 14.5" M4 at 200 yards. The United States military uses the 14.5" barreled M4s in quite appreciable numbers with very good results. That says enough for me.