So the issue is on localhost?

You confused me with your last comment on Firefox usage...

In any case, like I said, what you saw before is a side-effect. K2 does not require high memory limits because it does not perform any GD (or other memory demanding) operations. When you bumped the memory limit, a JCH error appeared. Disable JCH and any other "performance" plugins to see if things behave better. I mention "performance" plugins because I've seen plugins from other providers that would "inline" images on page load which can be very memory intensive on sites with lots of images.