This would be terrible for Gdrive upload speed, but it should be irrelevant as long as you are transferring Gdrive-->Mega and not the other way around, so not applicable to this spesific problem. I mention it as an apropo for later use. Just don't use this when uploading to your Gdrive (should be 64M at least IMO unless you have very low RAM).
You may want to enable debug output with -vv (replaces --verbose) and watch for a bit to see if you get a butt-load of server-errors or something. Definitely try it with default transfers/checkers like Animosity suggests.