Final answer:
The minimum initial requirement for buying 100 shares at $15 each is $750, following the FINRA Reg T margin requirement of 50% of the purchase price.
Step-by-step explanation:
The minimum initial requirement when buying 100 shares at $15 in a new account would typically be determined by the margin requirement set by the brokerage firm or the regulatory minimum if there isn't a specific brokerage requirement. In the United States, the Financial Industry Regulatory Authority (FINRA) requires a minimum of 50% of the purchase price of the securities when buying on margin, which is known as the Reg T margin requirement. In this case, if you're buying 100 shares at $15 apiece, the total cost would be 100 shares × $15/share = $1,500. Therefore, the minimum initial requirement would be 50% of $1,500, which equals $750.