Basically for this you want to play normally until the heavy comes, then just kite him around the room to slowly deal damage to him. It's a little slow and tedious but it's by far one of the safest ways to get through it. After the first heavy, continue with the payload section as normal. Stay far away from the enforcers as they do more damage the closer you are to them. Watch out for assassins, and remember to melee them as they land on someone to stun them. Eventually at the end there will be 4 snipers that will spawn, Genji can easily deal with them with his shurikens and deflect. The 2 heavies will not spawn until you take out the 4 snipers, so be prepared. As soon as you take out the last sniper, run back all the way to the distillery and lead the heavies around the room just like the first one. Again this is really tedious but it's super safe if you can get your team coordinated.