We had a few Mac users that are printing in a WC 7225 and they have the same problems. Printing are delays, sometimes it stays at queue. I already try to reinstall the driver, I used version 3.64 and the last one 3.68 driver for Mac, but it didn´t work. Everytime that I reinstall the driver (also by IP) it prints the test page and a few documents, then it got stock at the driver queue. I guessing that its something with Mac OS 10.10 because also we have windows users and they dont have that problems. Should I try to upgrade the Mac OS to 10.11 (El capitan) or try something else?
You mention print by IP, but not the protocol.
You will get very different results using LPD, than you will with HP Jet direct (RAW on a PC), and with IPP (Usually slowest)
My personal order of preference would be LPD > Jet direct > IPP, Airprint should never be used unless as a last resort.
It isn't 10.10 causing the problem because other locations aren't having the issue.
If LPD doesn't work, switch over to Jet direct, which is probably what the PC's are using (RAW).