Use a good braided line as your backing. You will be able to fit more backing on your reel and the smaller diameter will allow the leadcore to reach greater depths. With the longer leads you will be using with leadcore the braid gives a direct contact to the lure. I prefer using 20lb PowerPro as backing. Also, 18lb leadcore is usually a better choice because it has more lead in the middle of the line and it's the same diameter as 15lb.