I have used Defraggler for many years, along with CCleaner, on my internet (Vista) and DAW (XP) computers. I was advised to use it by a computer technician friend and haven't used the Microsoft defragger since.

Initially my all my drives,up to 1TB, took roughly the same time as yours but I now, on advice from some audio expert in the Sound On Sound magazine many years ago, do a quick defrag every time I use the DAW computer and it takes minutes.I do a full defrag every 2-3 months and that takes longer but nowhere near 15 hours thankfully,usually time to make a coffee, sandwich and wash up afterwards (I am well trained).

I have NO idea about any answers to your questions as all that is well above my computer knowldege but from my usage I would, and have, recommended the free versions of Defraggler, CCLeaner and Recuva to all my friends and all seem happy, well they haven't blamed me for any crashes etc....yet.

Hope this helps a bit,

Alyn