The solution to these long installs is simple, give the user an option:
1. One time 15 minute install
2. Progressive install - Install the 1st level to the hdd (say its 2minutes), then once the user completes a level or a section install the next section of models/scripts/sounds/video or whatever is needed to the hdd.
My idea isnt perfect, the first install may need to be up to 5 minutes but it might be better than a 15 minute wait.
Also developers should think about using the consoles resources more, especially when they arent being completely used i.e. a slightly slower method of installing data in the background when playing or paused, aslong as theres spare resources why let them go to waste.
I think developers need to be more imaginative in their software design, there are ways to work around these problems with a little imagination.