What's the longest butterfly race you could swim?

Is it illegal to do more than one kick between arm strokes? Not if it's a dolphin kick. I'm pretty sure you could dolphin kick an entire fly race without ever taking a single arm pull and be legal (as long as you surfaced before the 15m mark off each wall).

Is it illegal to do more than one kick between arm strokes? Not if it's a dolphin kick. I'm pretty sure you could dolphin kick an entire fly race without ever taking a single arm pull and be legal (as long as you surfaced before the 15m mark off each wall).