Do not ignore symptoms that may be due to low or high blood glucose. If you have symptoms that do not match the Sensor glucose reading or suspect that your reading may be inaccurate, check the reading by conducting a finger stick test using a blood glucose meter. If you are experiencing symptoms that are not consistent with your glucose readings, consult your health care professional.

Every minute data is measured, but data is stored at 15 minutes. What does the 15-minute reading represent?

This is the glucose value at the instant of the 15-minute time stamp.1

Reference

1. FreeStyle Libre flash glucose monitoring system User's Manual.