In terms of the depth, 1.5 is basically a point where a few HBOT doctors got together--specifically Dr. Nuebauer---not to be confused with Neubrander--and found that it was the best tolerated. There are a number of scattered studies in the field but most are typically focused on 2.0. Honestly, I think that there are probably better reasons to go to 2.0 then 1.5.
1.5 has just become 'set it stone' for no good reason at all, particular as it relates to autism. Just a bunch of conjectures, dogmas, and 'alternative explanations.' There are definitely reasons and needs to pursue alternative treatments, but don't treat the alternatives as sacrosanct. I think 1.75 will probably be better than 1.5.
Discuss autism diets and biomedical treatments of autism.