Problem: Fading LEDs because a 555 timer circuit was being used as a 15 minute timer.
The best solution would be to replace the 555 timer circuit with a digital timer, which uses an oscillator and a multi-stage counter to form at long time delay. The cost would be minimal and since no large capacitor would be needed, the circuit would not take up much more board space. The lesson here is that a 555 timer should never be used for times beyond about 3 minutes or so.
The circuit below is a 15 minute timer circuit.