I seem to be having a similar if not the same issue for a site that I’m currently developing. Hang times of 30 seconds and up, sometimes completely crashing the browser (Chrome), depending on how much content I have input into the repeater.
The repeater field is somewhat complex, mostly text fields, and a nested repeater with image uploads. I removed all conditional logic that it had as I thought that’s what was slowing it down but the issue remains.
This is all on a local setup, mind you, running the latest WP release (3.8) and the latest ACF (I also tried the current build on GitHub to no avail).
If I can contribute anyway to getting this solved, let me know.
Thanks,
Scott