10K SCSI or SAS is more than sufficient for a single user. Get a LSI Logic cached RAID controller. I used a 320-2X for SCSI RAID and 8708EM2 for SAS RAID. Invest in a highend controller instead of 15K drives.
SAS RAID 1 benchmark on 8708EM2 using Savvio 2.5" 146GB 10K drives
http://www.scsiraidguru.com/Computer..._SAS_RAID1.txt
SCSI RAID 1 with 10K 36GB Seagate ST336607LC drives.
http://www.scsiraidguru.com/Computer..._2drives_c.txt
15K are expensive and not needed.