Conventional design of DIY cloud chamber uses IPA and cooling down to -26..-33°C (sometimes even lower, down to dry ice temperature).
What could be changed in design approach to shift operating point closer to room temperature? -15°C is much easier to maintain with single-stage TEC compared to -26..-30°C. And something around 0°C could be easily achieved in large volumes. On the other hand - heating (if needed) is much easier than cooling.
For me it is not clear why optimal temperature is so low, and hence unclear whether I should pick liquids with lower or higher boiling point (acetone / water or other non-toxic solvents).