Migration stuck

I’m using an Ethernet cable and migration assistant to transfer data from my old mac (El Capitan OS). It initially said 3 hours to transfer but it has been 9 and has been stuck at 19 minutes for 4 hours. I’ve tried removing the Ethernet from both computers and re-inserting but nothing seems to work. I believe there is about 1/2 terabyte of data to migrate.

Is there anything I can do? What happens if I quit the migration?