Can you propose a control experiment? What will that look like? Cold, but not too cold chambers? Hot chambers?
So, the controls should also be treated with a series of 15 daily visits to a chamber that is simply the same temperature as its surroundings.
Having 15 daily visits worth of contact with study personnel, in a chamber that exists for a specific purpose, may have a big impact, regardless of temperature. But you won't know unless you use a proper control.
One great challenge in studying complementary/integrative health interventions is selecting the right control group, because practitioners will argue that the control is too much like the active treatment. (So, for example, a cold shower /might/ work, if the mechanism is the same, so it wouldn't be a great control in the initial proof-of-concept experiment.)