The Flex 15 has an HDD storage medium which is better than the SSD storage medium found on most 2 in 1 laptops that have been available for more than two years. HDD is a traditional storage drive which stores the information on magnetic disks. HDD drives are slower than other forms of storage such as solid state drives (SSD) and flash drives.
This laptop's storage medium (HDD) is in fact the worst storage medium across all 2 in 1 laptops that have been around for a similar time to the Flex 15.
Across similar types of laptop the best storage medium is SSD.