The Antique Clock Shop

The Story: In a narrow lane in the old city of Hyderabad, there is a small shop owned by a clockmaker named Rustam. He has been repairing and collecting antique clocks for fifty years. Every clock in his shop runs perfectly. One afternoon, a customer walks in and hears something delightful: all of the clocks in the shop are chiming at the same moment. Rustam explains that this happens once every so often, when all the clocks' chiming intervals align. The customer looks around. There are three grandfather clocks. The first chimes every 15 minutes. The second chimes every 20 minutes. The third chimes every 30 minutes. 'They all just chimed together right now,' Rustam says, glancing up from a gear he is polishing. 'When will they all chime together again?' The customer thinks for a moment, then smiles. The Challenge: The three clocks chime at intervals of 15, 20, and 30 minutes respectively. They all chime together right now. How many minutes from now will they next all chime simultaneously?