As of my last update in January 2022, there has been no official announcement or credible report indicating that Pakistan has purchased F-35 fighter jets from the United States for $1.5 billion or any other amount. It's important to note that the F-35 is a highly advanced and expensive aircraft, and any potential sale of such aircraft between countries would typically involve significant public attention and diplomatic discussions.
However, please note that my information might not be up-to-date. I recommend checking recent news sources or official statements from relevant authorities for the most current information regarding defense contracts and purchases.