For a conference such as Revive15, that is, not work, professional or academic, I think the evaluation should be a light touch, but even so, people should have an opportunity to cover the main parts of the conference.
- Content: main speaker/s, workshops (perhaps one line for each workshop)
- Video breaks
- Meeting people
- Hospitality (did you feel welcomed, cared for, respected)
That should cover it.
All on a four point Likert scale, with a line for optional comment.
Then, of course, sex, age band, educational level and income band (because it indicates occupational attainment and therefore general capability).