You're not a bank, the details don't matter. Don't even bother with getting anything in writing from someone who is over leveraged, because you're already never getting that money back in any court regardless since the other creditors come first.
He said I can make money by apply for loan against property, and loan to him and pocket the different.
You never give loans to someone that you're not completely prepared to write off. You absolutely don't give loans with loans (unless you're a bank and getting those loans from a central bank, which I doubt you are).
A friend offer me a investment opportunity at 15% annually, is it too good to be true ?
He was my coworker. I know him at work for years. It is unlikely he take money and run away....