Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Mine (2013 rMBP) is almost always cool and silent about the only thing that causes it to heat up significantly is gaming, the newer ones are just as good by all reports.
 
High running temps are more related to the 15" rMBP, the 13" in general runs very cool unless it`s under very heavy usage.

Q-6
 
Is there a reason why the 15 gets hotter?

Quad Core CPU & dGPU, adds up to a much larger thermal signature. The 15" rMBP is a very powerful Notebook, equally there is a trade off with associated fan noise/intrusion and elevated temperatures reached far sooner, even under moderate use.

Q-6
 
The fan on my 2015 rmbp 13" has only turned on one time and that was while editing a 1080p gopro time lapse in imovie. Other than that it runs very cool, only getting warm when used for long periods of time.
 
The fans on my 15" spin up more often but at the same time, I have yet to actually feel my 15" MBO get hot. The fans do a very good job at keeping it cool to the touch. Even after an hour of converting some videos, the case barely felt warm.

There are two fans on the 15" and one one the 13". The fans on the 15" continuously spin, when cooled at about 2000RPM or so, and on the 13", they frequently turn off.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.