On my system with VirtualBox 5.0.24 recent image (from https://cloud-images.ubuntu.com/xenial/current/, dated 20160725) with enabled UART boots till "Btrfs loaded" string in 105 seconds, and with disabled in under 7 seconds.
While enabled UART change fixes booting, it significantly reduces likelihood of image usage due to very slow boot speed.
Looks like with released fix VM boot speed has decreased drastically: https:/ /bugs.launchpad .net/cloud- images/ +bug/1567265
On my system with VirtualBox 5.0.24 recent image (from https:/ /cloud- images. ubuntu. com/xenial/ current/, dated 20160725) with enabled UART boots till "Btrfs loaded" string in 105 seconds, and with disabled in under 7 seconds.
While enabled UART change fixes booting, it significantly reduces likelihood of image usage due to very slow boot speed.