I seriously doubt that your "system" is as much as 15gb
My XP-Sp3 Notebook "system" is not quite 6gb, and I know because I've isolated all my "data" to seperate partitions.
even my dessktop system is shy of 13gb.
I'd honestly recommend downloading and running a program called CC-Cleaner before you migtrate to your new drive....
your system is probably bloated with "temp" files that Windoze never deletes.
My point about the bigger drive was about anticipating unanticipated needs, you might suddenly decide to carry your entire video collection around on your notebook...
then you'd have to buy a new, larger HDD, when you could do it NOW for just a few dollars more.
I wish my Notebook was new enough to use a SATA drive because I see the WD 640gb drive for $75(US)...
My point aobut the Better quality drive is that there are two kinds of HDD, those that have failed and those that will fail.
It's a mechanical device and nothing lives forever.
I haven't had that many drives fail, but three of them have been
notebook drives, and I've learned my lesson to create cloned backups of my Notebook OS drive partition, because reactivating the OS is never any fun.