Marc,

15* spindles will make it easier to drive but will not provide as much initial steering going into the corner. The 10* spindles will allow you to enter into the corner, will make the steering a little more sensitive and you will loose some mid-corner steering on power. You can play around with the kick-up in the front to find a happy middle depending on which way you go. I like the 10* spindle over the 15* for the track's I've been running on.

Hope this helps,
Mark