Thanks for the replies.
I just received another spare disk. Right now, I am rebuilding disk 14 with the precleared one I already had, and preclearing the new one.
Once disk14 is rebuilt, I will rebuilt disk 3 with the new precleared spare.
I didn't know you could data rebuild with an unmounted disk in the array, but it is going fine at the moment, will complete in 3.5 days.
Thanks again for the help, I will keep you informed on how it goes.