I wouldn't recommend 10 but 15 should still work fine, that's what I set mine to before I upgraded computers and it worked fine.

Judging by your system specs though you should get better fps than that...my new comp is about the same(Q6600, XFX 8800 GT 512mb DDR3(Alpha Dog edition with slight overclock) and 4gb 800mhz DDR2 dual-channel G-Skill ram(on sale for $80 at newegg right now, VERY good deal for 4gb); somethin tells me there's something else running that's eating performance or the HD/Mobo simply can't keep up; HD speed and how you installed your WoWs can have an effect as well...

1 dir or multiple dirs? If multiple, is it simple copy/paste or are the dirs' Data folders Sym-Link'd? Multiple, non-linked install dirs = bad performance vs the other two options, IDE or SATA drive? SATA is a much faster reader and the RPMs on the drive regardless of which it is make a difference too, how fast it reads the data.