A property 'com.openexchange.preview.cache.enabled' has been introduced. Excerpt from '/opt/open-xchange/etc/preview.properties':
# The switch to enable/disable the preview cache
# Default is true (enabled)
com.openexchange.preview.cache.enabled=true

The switch enables/disables the cache globally. Additionally the property can be set via config cascade for a more fine-grained control.