At 15 chairs per hour, that's only $60.00 per hour at $4.00 per chair, not including travel and set up.
For some locales, that is as good as it gets. For most, it is rather cheap.
The choices are either raise the rate, or raise the production to be more profitable.
In this demographic, $100.00 per hour is median. Granted, less for high volume. But look at least for making $75.00 per man/hour. You have your overhead to consider, which is going to bring the profit down.