Hi Nuka,
Thank you for using the Xerox support community forum.
I would suggest that you review the following page for possible solutions. WorkCentre 6027 Support & Drivers
I searched for "wireless" and "slow scan" and "Mac wireless slow" and found many articles.
If those do not help, and because you have the problem on your WorkCentre 6015, you may consider contacting the product support experts by email Fast Track to the Expert or by phone 1-800-835-6100 (U.S. & Canada)
If you are outside the USA you should contact the local support center in your area which you can find here:
http://www.xerox.com/about-xerox/contact-us/enus.html