I tried the same thing on one of my linked clone VDIs:
-Win10 1909 VM
-ESXi 6.5
-Horizon 7.9
-VMFS 5 Datastore (It was on VMFS 6 previously, I changed to a VMFS 5 on another suggestion from someone, it may have helped slightly but still was taking far too long for a simple reboot)
Changed the virtual disk to bind to a SATA controller instead of the default LSI SAS controller. Took my boot time from 15 min+ to 15 seconds. I'll be changing the master image to the same config and test with an entire pool.
UPDATE:
After changing the controller on the master image to a SATA controller, my VMs got stuck in the customizing state indefinitely. After a frustrating all nighter, several hours on the phone with VMware (who blamed my version of Win10 and Horizon), and totally rebuilding my image, I figured out, in my case at least, I HAD to have a SCSI controller added to the parent image, even if my disk was attached to the SATA controller.