Found the solution:
adb reboot bootloader
Then boot it into recovery and then:
ubuntu-device-flash touch --device=mako --server=http://system-image.ubports.com --channel=15.04/stable
This ends with:
2018/02/26 21:42:20 error pushing: adb: error: connect failed: no devices/emulators found
But after rebooting it it is up and running 15.04 without any problems
Sorry for not trying harder before posting above!