All of my HA have had no more than 3 HA. I can tell you that at HA 3 you will be competitive, but when you encounter a truly skilled HA opponent, he will dominate. That extra HA skill is vital to making longer distance shots.
The good thing about making an HA build with only 3 HA, is that you can hybridize and pick up nice things like powerstrike and athletics. This allows you some melee capability and foot archer ability.
It comes down to what you want to do, really. If you want to stay pure HA, go with the 15/24 build. If you think you might get tired of only being good at HA, then consider a more hybridized build.