[J. T. Toad]

I'd pick up an under-gravel filter and a good air pump and not worry about the external, not for 15 gallons. Remove the live plants, at least for now.

It should never really get that cloudy, whereby cloudy is a relative term.

The fish actually need very little food. Anything they don't consume within 2 minutes is a waste. Feed once to twice a day, at most, and skipping a day every now and then doesn't hurt.