I don't think I'd shoot that big for just monitors. A ten and horn self powered (or better, a pair!) in pretty close might be all you need. Unless you are providing LH bass, a 15" is a bit overkill, especially as your sound-man (if he's any good!) is going to roll off quite a bit of your bottom end anyway (to not clash with the bass player).

In fact, a SMALL OMB rig (small self powered mixer, two small top cabs, forget the sub) might be perfect. And you probably already have THAT kind of rig.....