Migrating from old MacBook pro to new MacBook Air

Hi, I am trying to migrate from my old 2012 MacBook pro to a New MacBook Air, it starts migrating and says it has about 3 hours to go and after about an hour it still looks like it is migrating but it doesn't move along and then increases its time to completion (10 hours). I am migrating using my Fixed Wireless NBN internet.

Thank you

Sharon