edit: With 100% less snark the trillions in the stock market is illiquid, while $15 Billion over a short period of time (as to benefit of the 5 years of growth) is not a trivial thing to accomplish without changing prices when those trades hit the books.
I don't really understand your claim with respect to liquidity, either. Be precise. Are you talking about slippage? Do you really think someone parking billions of dollars in the market would do so without staggering it to avoid prices moving against them? It's not like he's just going to throw $15 billion into the SPX and hope the daily volume adjusts without a problem.
15 billion remains not a lot in the grand scheme of things.
Further adding value by mentioning there is an art to trading an illiquid position
Michael Dell would have needed to make special considerations than just hitting the sell button to get prices remotely close to the last things printed on screen.