Please read the following documentation before submitting a request to the API.
https://fencosoft.github.io/

A note about requests: Request quantity is limited to 15,000 records OR a 2mb response size, whichever comes first. If the API recognizes that your response payload might exceed 2mb it will respond with a suggested number of records that will result in less than a 2mb response size. As the data results are based on randomized values, the quanity suggestions are a “best guess” effort that err on the conservative side so that you can maximized your results without exceeding the threshold.