He might not be speculating, he might be holding a bunch of SPY shares and simply withdrew $150k as a margin loan so he can make a purchase on a house or car but not pay taxes on gains yet from selling his shares, opting instead to pay off the loan over time through regular deposits.
He is still speculating on the SPY and his ability to pay off the loan depends on how the SPY holds its value. A market crash would hurt his ability to pay off the loan.
No it doesn’t. His loan is the same no matter what SPY’s value is. He pays it by depositing money he earns from his day job, not by selling shares. If SPY crashes very hard his broker may force him to pay the loan very quickly, either by adding more money or by selling off his shares to cover the loan.
