Eh, I find it funny how many people diss Izzy considering on other threads most posters rave about names such as Alfie or Albie, which are just as nicknamey as Izzy.
That said personally I can't stand nicknames used in lieu of the real name. But that's just me so if you love it don't let that stop you.
To be honest I'm not that keen on Orla either. It makes me think of a French novel called The Horla. Beyond that I just don't like how it sounds. But again, just my opinion and I'm clearly in the minority is !
In my experience you know you have found The Name when you stop looking for alternatives, so if Orla does that for you then go for it !