Dell Laptop Slower to Boot with Core Isolation Enabled

I have a Dell Inspiron 7537 laptop. I just updated to the latest consumer release of Windows 10 v1803 (17134.112).

I've been experimenting with the new security feature Core Isolation (CI). The laptop (SSD based) does a cold boot in 15 secs with CI off. However, the boot time increases to 45 secs with CI on. The PC is otherwise responsive enough in everyday use.

Why does the CI feature slow the boot speed? Note my laptop has the latest Dell BIOS offering protection against the Spectre vulnerability. I'll probably keep using the CI feature anyway since it provides useful additional protection.

Bree said:

Core Isolation is on all the time, it's the Memory Integrity part that you can turn on and off again. You may have noticed that once turned on the switch is greyed out and 'Managed by your Administrator'. It takes a .reg file to turn it off again...
Turn On or Off Core Isolation Memory Integrity in Windows 10 | Windows 10 Tutorials

Dell Latitude 7440 here, like yours it has the latest bios. It has an HDD, so will be slower than your SSD.
You can measure your restart times with this...
SevenForums | Restart Time - Windows 7 Help Forums

With Core Isolation Memory Integrity turned on my restart time is 96 seconds, with it turned off its 76 seconds. So turning it on adds 20 seconds to my restart time.

I had to use the .reg file method to turn off CI. Why doesn't MS trap these obvious problems?

I'm still curious why setting CI on slows down the cold boot time.