The reproduction speed of a certain type of kombucha doubles every day. If the kombucha can cover the entire surface of the tank after 16 days, how many days will it take to cover half of the surface of the tank?
某种红茶菌的繁殖速度是每天增加一倍，若经过16天红茶菌能长满整个缸面，那么长满半个缸面需要多少天．
<gadget id="calculator">16 - 1</gadget>
<output>15</output>

<result>15</result>