1-15/20 is the hardest part imo.

Once I get to barrens and XR, my guys start ripping through content.

edit : also IMO, skip any collection quests that aren't part of a chain of quests that have a good amount of fast quests you can knock it, otherwise its not worth the effort and just skip them imo.

Just do a few instance runs and will more than make up the quests you skip.

if its part of a good chain though, I do them.