How strange. I know lag can happen when you run a mod in minecraft while vox-l is still open and running in the background, if there's alot of data on your account (like lots of large mods on your account or lots of things in your vox-l world) or if you invite others to your minecraft world. Let me try resetting your world -- let me know if that makes a difference.
Are you trying to run a specific mod? If so, what's the name of the mod?