Not too good to be true, but too good to be low risk.
15% ROI is definitely possible. Him screwing up and ending up bankrupt is also possible.
The red flag for me is "I know nothing about business" - you can't judge the risks. You should absolutely not invest money you can't afford to lose into risky stuff like this. In particular, taking out a loan just to loan the money to your friend would be a really stupid idea, and if he asked you to do that, he either is stupid, reckless, or doesn't care if you get hurt.
I'd only consider loaning my own money with which I can afford taking the risk, and only if he could plausibly explain what he's doing, and I felt like I can understand it and be confident that he can pull it off. I'd consider it a high risk investment on par with cryptocurrencies.
Given that you don't seem to fully understand and there are other red flags: stay away.