Some notes on getting 15.10 Mini up and running:
During installation (which is text-based), choose the "basic" MATE Desktop option
After rebooting, it starts in the terminal.
What I did to get the desktop going:
$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo apt-get install ubuntu-mate-core^
$ sudo apt-get install lightdm
(Or install your choice of display manager)
$ sudo apt-get install lightdm-gtk-greeter
(The corresponding greeter)
$ systemctl is-enabled lightdm
(Should say enabled)
$ sudo shutdown now
Upon restart, should see a basic graphical login prompt. Login as normally done in MATE.
Disk usage is around 3-4 Gb. Memory about 280 Mb at rest.