In that screenshot, the query has only been running for < 20 minutes. If you're killing the process and restarting it, you're potentially just scrapping all of the work.
There's nothing that we can really do to speed up the process. This is internal to how MySQL rebuilds tables. You can potentially look at making sure you have MySQL as optimized as possible with respect to I/O, but otherwise there isn't a ton that can be done.