Hmmm... I will take a shot at this one...

My thought is that take one fuse and light it on both ends. This way, you know the burn time for this fuse is 30 minutes, no matter how quickly it burns along any point of its length.

As soon as this fuse burns completely out and the two burning points meet, light the second fuse at both ends, and in the center. This should give you the last 15 minutes. Edit: Hmmm - is this 15 minute part valid? I am not so sure now...

Insert Edna St. Vincent Millay poem here...