What version of Photoshop are you using and do you have all the updates? I ask, because ISTR that preview was a JDI fix making it heaps faster with GPU acceleration. I did just try to stop it, but was unable to find a workaround. I'm seeing up to two seconds to refresh the preview going between 30k and 5k pixel square. This is with a six core 3930K with GTX570.
I did wonder if the preview zoom size would make a difference, but it doesn't, and always defaults back to 100% the next time you open the Image Size dialog box. I tried hold down the space bar (which works with some plugins). Escape just cancels out. There are no panel options I can find.
No way to switch to the old-style dialog.
I guess you have CC. You can also install and activate CS6 with your membership and use the legacy Image Size box if that's all you need.