I would recommend the featurette first. The audience should have the main feature film resonating in their minds after it is over. If a featurette is directly after the film, it messes with that concept.
Think of it like a chunk of previews. If the previews for other films are after the feature, the viewer will remember more about the previews and less about the feature film than if the featurette is first, then the feature. I hope that helps!