You will be very lucky if you have don't have at least one dodgy folding mirror on your S15! If you have thought that you'll have to buy a new wing mirror to sort the problem - you're wrong. Nissan, in a rare moment of forethought, designed the wing mirrors so that the electric mirror motor and power fold motor can be replaced separately, thus saving you a shedload of money.
Unlike the S14, the S15 has a replaceable air conditioner/ventilation filter. Judging by the state of the old filters which have come out of others cars, I'd say that they are very rarely changed. There is one simple way to tell almost for certain if this is this case. It will be evident as you read on.