Flip it. If you're gong to pay someone $15/hr, you better have something that needs doing that's worth that much to you.

One way to look at employment is that it's your responsibility, as the employer, to know how much a job is worth to you; it's their responsibility to perform that job.

If you're having people do something that's not worth what you're paying them? I would say that sounds like you're not running your business very well.