Migration Assistant Hangs at End?

After each system upgrade I have to force quit the upgrade at the end because it takes hours/days. Now I have one Gb of data in:

/Library/SystemMigration/History/Migration-766633E7-8821-44F1-A5BC-D2602BAED72B/ Quarantine Root/

can I safely delete this waste of disk space?

Ok, my iMac's spent about 2 & 1/2 days between Friday night and Sunday morning doing a series of failed migrations and one successful one. The source is a late 2009 27" iMac 1TB machine (OS X El Capitan) with about 550GB of stuff so lots to move. The destination is a brand new 5k Retna iMac also with EL Capitan.

I won't go into detail about the failures because they don't matter but this is the setup that finally worked.

1. I Went into System Preferences -> Energy Saver on the source and told it never to sleep and never allow the hard drives to sleep.
2. Plugged a CAT (Ethernet) cable between the source and the destination
3. Ran the Migration Assistant and walked away.

The Key was step 1 making sure that the source didn't sleep because I'm pretty sure during the other 4 attempts, the source went to sleep as the time to complete went into the hundreds of hours.

It took about 12 hours total and the end was signified by the destination computer rebooting, the Apple Chord sounding and some additional steps to start using the computer.

I migrated a MacBook Air to a Macbook Pro. Same initial problems as the thread. I was using a Thunderbolt cable to link the two machines. After thinking for a while, it crossed my mind that WiFi might be interfering so I turned it off on both machines. After this it took only 30 minutes to complete the migration.

Well, here's my experience with Mac migration. Slow, slow, slow and, in the end, unsuccessful. Be patient, forums like this advised, so I was, but after more than 48 hours, my data still hadn't finished transferring. So I shut it down, opened the new external storage device I'd bought with my new iMac and used Time Machine on the old iMac to save the data. (My previous time machine storage device had quit working). I'm now in the midst of transferring data and documents to my new iMac. I expect using Time Machine and the external storage device will be more successful than connecting the 2 computers by Ethernet.

Update: Migration using Time Machine wasn't as simple as I'd hoped. It created another user on my new Mac. Then I had to go and learn how to transfer files from one user to another.