Two fragrant with uneven texture, each can burn for one hour. How can I judge for 15 minutes?

The first step, two incense at the same time lit, a fragrant two points, B incense a point.

The second step, a incense burning time spent half an hour, at this time B incense also remaining half an hour length

The third step, from now on, B incense at both ends of the point, b incense burning time is 15 minutes.

Summary: One, the meaning of a incense is to define a half an hour B incense

Two, a incense can burn for one hours, the premise is lit from one side, this is a hidden precondition.

Two fragrant with uneven texture, each can burn for one hour. How can I judge for 15 minutes?