I've been running FSLogix and Apex One for a while now, and have never seen the issue you describe. Here's how it's configured in my environment:
Environment
XenServer 7.1 LTSR CU2
CVAD 1912 LTSR CU2 (using PVS, non-persistent)
Citrix App Layering
Windows 10 1909 (FSLogix Apps 2.9.7349.30108)
Windows 10 20H2 (FSLogix Apps 2.9.7654.46150)
Apex One Settings
Trusted Program List:
- C:\Program Files\FSLogix\Apps\frxsvc.exe
- C:\Program Files\FSLogix\Apps\frxccds.exe
Scan Exclusions:
- C:\Program Files\FSLogix
We exclude all .vhdx file scanning on our SAN share, as well. Are you running TCacheGen as the last step in your sealing process for Apex One? I highly doubt that would cause the 15 minute delay, but it should be done regardless.