I'm a (happy) user of the F14 Xfce Spin and am still undecided about whether to upgrade to the F15 Spin. On F14 Xfce, I have not experienced any of the problems you describe, so unfortunately I can't offer good advice based on firsthand experience.
However, in case you don't receive any replies here in the Fedora Forum, I would like to suggest a Plan B: the Fedora xfce
mailing list. Some of the Fedora Xfce developers (such as Christoph and Kevin) participate in it, the atmosphere is friendly and it is a low-traffic list. If you register for it, someone there might be able to help you.
Information on the mailing list is available here:
Another thought (which you may have already considered): Are you sure that you installed from a good .iso? Did you check the sha1sum / md5sum, installation medium, etc.?
There are instructions for verifying your download here: