I had a problem like this a long time ago, and I think it is caused by the option "Update interval in seconds" near the bottom of the Wordfence options page. Try changing it to 5 seconds, save the options, then go to any other Wordfence page, and see if the ajax requests in the logs are then spaced out by 5 seconds. (If you stay on the Options page after saving, that page would still be doing ajax requests at the original speed until you leave it and come back.)
I have had mine set at 5 seconds for a long time, and haven't noticed any problems. I don't use the Live Traffic view anymore, which is probably where the difference would be most noticeable.