Chris, there is no silly question but there are unclear answers that beg further explanation. If I'm not clear again, I invite more questions.
Your proposal of using 15 amp fuses sounds ok to me. Think of auto power in terms of watts (volts times amps). In household wiring, 15-amps produces over 1,000 watts but in automotive circuits, 15 amps produces only 180 watts (less than two 100 watt light bulbs). The situation was even worse when we used six volts because 6volts X 15amps = 90 watts. We are forced to use high amperages and large wires to get serious electrical work done in a car. - Dave