Soy wax is a softer wax and doesn’t take as much heat to melt. Therefore soy candles generally need a cooler burning wick depending on how much fragrance oil and dye is used, the more used, the hotter the wick most likely that you’ll need.
So soy candles burn longer because the wick is not burning as hot and therefore the wax is not burning off as fast as regular paraffin candles. This is why soy candles burn twice as long as regular candles! Isn’t that awesome?