The Flex 15D has an HDD storage medium which is better than most notebook PCs that came out more than two years ago. Most notebook PCs of a comparable age and spec to it have an SSD storage medium. 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.
An HDD storage medium is actually the worst storage medium across all similar spec portable PCs that were launched around the same time as the Flex 15D.
An SSD storage medium is the best storage medium across comparable types of notebook PC.
If the storage medium of this notebook PC is not good enough for you then you might want to look at the Lenovo Yoga (SSD), or the HP Pavilion x360 (SSD).