Wall Street Skeptic Barry Bannister Sees 15% Decline for S&P 500 - Barron's

1. Bannister warns of 'very extended valuations' in current market. 2. A potential economic slowdown could spike a market selloff. 3. Consumer staples, including Costco, are performing better than healthcare stocks. 4. Market rally driven by speculation could eventually end, impacting stocks. 5. Bannister recommends investments in defensive sectors like staples.