Complex sentence: Scandlines' ferries have more than 70 daily departures from each harbour, every 15 minutes during most of the day, and even every 12 minutes during the most hectic summer weeks by the use of an extra ferry.
Split into simpler sentences: Scandlines' ferries have more than 70 daily departures from each harbour, every 15:th minute during most of the day. This frequency can be reduced down to every 12th minute during the most hectic summer weeks by the use of an extra ferry.