15% of that is paper money, heavily levered against. If he tries to sell even 2% of that in order to turn it into actual real money, the remaining 13% will be worth less, because a sell-off will lower the stock price.
Of course, just selling a single stock will lower the price of other stocks. But the dropoff is nowhere close to what you are implying. He has sold lots of stock over the years and somehow Tesla stock price didn't drop that much.
I feel like you used 'worth less' to imply 'worthless'. But this is far from the case, 13% would still be a gigantic pile of 'money'.
