Where are you feeling the heat? What was the weather like, or how warm was your garage?
I used my G15 a couple weeks ago to polish out my car and never felt any heat at all, granted it was only in the 60's~low 70's at the time, but I didn't feel anything. My old HF DA would get hot after extended use and in the summer when the garage was in the 80's it would really heat up.