No, the punchline is "I can't afford this house." It's humorous because the preceding story seems to build up to some anecdote about how having some money right now is less important than having more money later, or some other overdone trite non-observation, but it ends with the orator subverting your expectation that he can easily afford the house by admitting that not only can he not afford it, he in fact has no money and must find a way to make the entire $15,000,000 within one year.

Like all jokes, it's not funny if you don't get it, and if you only get it after someone explains it to you, it still won't be funny.