LED's do not generate heat. You wire a resistor in series with them to ensure that the voltage they see never goes above a certain level, and this controls whether they heat up or not. An LED *should* have virtually limitless lifespan, and it is more likley that the other components of the circuit will give way before any LED will.

And you only managed 15 minutes? She won't be your GF long with that kinda performance. Although, if only YOUR legs were touching the ground I'd rescind that comment