I don't know a lot about Lufthansa routes, but I would be surprised if they took 15. I am guessing that it will be broken down into some firm orders and the rest options. I fly LAX-FRA once a year, and when it's the 744 it's always full. I'm sure FRA to JFK, Tokyo, Delhi, and Singapore are too, and could therefore use the added capacity.
But I am especially curious about one thing. Not only is the added capacity a challenge to fill on the A380, but what happens when an airline is flying one on the same route with another airline that has also upgraded to an A380? For example, what if LH wants an A380 for FRA-Singapore, but SQ is also using one on that route? Doesn't that make it even harder to fill those birds?
It is not enough to be rude; one must also be incorrect.