Well, I'm not a Badger employee... so don't take this as official word....
On the 3155 question, I honestly don't know. I'll be glad to ask, and pass along what I find out though.
My understanding in regard to where it is relative to the 100LG and Renegade-Velocity is that it is a more affordable gravity-fed option for the hobbyist.
You might find this chart on their website interesting- it classifies where they feel each airbrush falls in terms of which one is recommended for which mediums and area of use. They actually recommend the 155 over the 100 for hobby use! Of course I'm sure they owuld say to each his own, but this is certainly a chart I will refer folks to- I'm sure many would find it helpful!
http://www.badgerairbrush.com/Application_Chart.asp
Like I said.... my word certainly ain't official. I'm just a forty-ish, overweight goofball who has a new toy!
Jon Bius
AgapeModels.com- Modeling with a Higher purpose
"For I know the plans I have for you," declares the Lord, "plans to prosper you and not to harm you, plans to give you hope and a future." ~ Jeremiah 29:11