There's no optimal minimum wages. All artificially set prices will create unfairness since they won't result from a consensus by directly implicated economic actors. Labor is worth what it's worth. If someone earns $10/h and is bumped to $15/h, it'll be unfair for the guy doing the more difficult job being paid $15/h. That person will either have the trouble of asking for a raise or changing job to do the easier one since it would pay the same amount.

Money ultimately has neutrality. Artificially set prices are just unnecessary hurdles in price valuation.

Minimum wages are used to try to fix an unrelated problem. Laborers are forced to pay non-producing owners of capital, and it impoverish them. So they try to artificially bump their pay. But the solution isn't that, it's to stop forcing them to pay non-producing owners of capital.