I'm not a fan of straight 15 gauge spokes. Most hubs are drilled for 14 gauge spokes so the smaller diameter 15 gauge can wiggle around in the hub flange holes too much. My favorite spokes to work with are 14/15/14 gauge. If you want to save a few bucks, use straight 14 gauge.
If you are going through the trouble of relaceing the wheel, make sure that your rim is in excellent condition and is a brand and model that has a good reputation.