To low, ie below 25' = tail strike in the event of OEI, too high, ie above 15' = risk of losing sight of the deck during a reject, especially at night, and arriving off the deck, colliding with the structure of falling off the side. Take your pick!
I would also ask you how you know when you are at 15' or 25'. Hard to judge visually especially at night. The EC225's radalt is not bad, but there is some lag (although AH denied it when I queried it!) so IMO when the radalt says 15' or 25', you are already well past it if you are flying the manoeuvre dynamically (as you should be). It seemed to me that an indicated height of 15' was not too bad, probably nearer 25' actual!