Hi all,
Scenes are cross-compatible on all Qu mixers, assuming the firmware on the target unit is equal or higher than the firmware on the unit where the Scenes were originated. As Andreas says, only relevant settings will be recalled, e.g. Qu-16 will discard any higher Input channel, any Group, Matrix or extra SoftKey. Overwriting Scenes or Shows on a Qu-16 will likely result in the settings for those higher Input channels, Groups or Matrix being lost, so I recommend you keep a backup of the original memories.
Hope this helps.