Its basic accounting. If you have to pay someone $15/hr, they better be providing at least that much value back to you, otherwise you're running a charity
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.