My suggestions are to seek a phone call or some kind of contact with the teacher, without the acknowledgement of your child. That way, you are not undermining the teacher in front of your child. I would state that you are concerned about your child marching in 115 degree heat, especially for an action that he is not involved. From my personal experiences, schools are now teaching teachers not to use group punishments in their classroom (again, this is just from my schooling and my experiences with schools, and it doesn't apply to every school). If after talking to your child's teacher you do not feel that this is solved, I would go higher up to the principal....this is only after going to her first. Will she think you are a problem, maybe. Will she at least think about what you are saying, I would hope so. If she is childish or a complainer, she will go to others and tell them about your meeting; this might prompt a statement from them like, "Are you really making the kids walk outside like that?" Just be up front and compassionate with her about how you are worried about the heat and this group punishment, which it appears to you that these troublemakers are not caring about how this affects the rest of the class. I am sure she is trying to get it across to the class that she will not tolerate this misbehavior, but in my opinion, she is going about it the wrong way.
I, personally, would not tolerate this form of punishment with my child....but going to her and explaining your concerns would be the first action that I would take....