Bazhong bus No. 5 departs every 5 minutes, and No. 4 bus departs every 3 minutes. After the two buses depart at the same time, how many minutes have passed before they depart at the same time?
巴中公共汽车5路每5分钟发车一次，4路车每3分钟发车一次，这两路车同时发车以后，至少经过多少分钟又同时发车？
<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>