Fiora's passive needs to be less persistent and/or less consistent

right now at all ranks her passive takes .5 seconds to identify, lasts 15 seconds, and when she bursts it or it times out she immediately identifies another one. thats pretty dang uninteractive if you ask me. keeping from getting hit for the duration wont make it go on a cooldown for a while (and even if it did 15 seconds is a long time), when you fight her and she procs it it doesnt go on a cooldown. im not saying it should be gutted, but it should have a cooldown until it comes back up again that scales down with her ult level and it's refreshed if she procs it. thoughts?