Equating your job listing with minimum wage will not provide a similar wage for a self-employed freelancer. Self-employed freelancers are responsible for their own equipment, which costs money, have no employer-covered insurance, which costs money, pay their own social security, which costs money, have administrative obligations that cost time (and thus money), and on top of all that they take an inherent risk of instability working as a freelancer. All of those different things drive up the hourly wage for self-employed freelancers. I personally live in Western Europe and I’m not 100% familiar with what costs freelancers in NA come across, but I can tell you that, living in a town with not a particularly high cost of living (i.e. not a big city) assuming a stable (which it rarely is for freelancers) gross income of 2400 USD a month, I’d not be able to cover my professional costs, pay my taxes, insurance costs and after all that still make my month to month living costs with the current inflation situation.
You’re also simultaneously calling this job “a full-time paid internship” and “a contractual $15/hr full-time freelance position”. Which is it? If they’re working under a freelance contract they’re not an intern, they would have costs and responsibilities besides working for you that no intern should or would have. An intern “working as a freelancer” would, extremely importantly, lose all labour rights/protections all workers deserve (Though I’m not sure about intern labour rights in the US).
To me, it looks like you’re trying to hire someone to work for you full-time, but without having any administrative obligations yourself, avoiding the responsibilities that come with being an employer, while at the same time offering (in a lot of cases below) minimum wage. 15$/h for an intern is great, especially considering interns often don’t even get paid at all, so this is very commendable, I think it is unethical for companies to not pay interns. However, 15$/h for someone who’s self-employed would not cut it, unless I suppose they’re living in a low-cost country, I don’t know much about that though.
I understand you’re trying to limit costs, but if you’re looking for an intern who can learn and build experience working for you and offer limited assistance in workload, great but hire them directly and offer them the relative safety that workers would have. If you’re looking for someone to do qualitative work for you without you having to offer them a stable employee position, I wouldn’t conceal your low hourly payment under the veil of an internship.
Here’s a decent resource that can help you give an idea of what the rates of freelancers are, particularly in Western Europe. The page is in Dutch, however, you should be able to right-click it and translate it in your browser. https://www.freelancenetwork.be/nl/freelance-tarieven
I hope this helps you give a better idea of why the rates of freelancers are what they are, and why 15$/h is not an attractive offer for someone who is self-employed. Keep in mind that most of my insights on this come from being a self-employed freelancer in Europe, and there might be slight differences in the US, that said there’s a lot of overlap as well. I hope this clears up why this offer is probably a bit controversial, and feel free to let me know if anything I said is unclear (: