In the Misc tab of the Properties window there is a setting at the bottom that says something like 'Cells to Load'. It's 5 by default, change it to what you want. Just know that depending on your computer this can rapidly cause lag.
Also, if you're editing one small 5x5 area, you just don't want it reloading, you can uncheck 'Allow Render Window Loads' in the Render tab of the Properties window. Then no matter where you pan it will keep that 5x5 area of cells loaded. To make it load, simply check the box again, hit apply, then hit f5. Or you can just hit F5 and it will load the 5x5 grid that you're centered over, but still wont load as you pan. (Until you recheck that setting)