Americans are all about that $1.5 million nest egg for retirement — living easy with golf trips and fancy cars. But "Shark Tank" tough guy Kevin O'Leary says to hold on — you can retire with just $500,000 — a big difference from the $5 million he suggested last August. According to Mr. Wonderful, the key is investing smartly and maybe scaling back your spending after you clock out for good. Don't Miss: The average American couple has saved this much money for retirement — How do you compare? War