Macbook Pro overheating issue

Fan speeds are related to the temperature of your laptop. If you're just interested in monitoring the temps, iStat Menus ($16) has an excellent temperature monitor that sits in your menu bar and can track any of the dozen temperature sensors built into your MBP.

There are a few apps which purport to allow you to control your Apple laptop fan speeds.

EDIT: Updated Aug 2018

• Macs Fan Control -- $15, last updated Mar 2018
• smcFanControl -- Free, last updated Oct 2016, many users report that they can set fan speeds high, but not low

I've found that the best solution to keeping my computer cool and the fans off, even when really tasking the processor, is to put it on a little stand to allow plenty of airflow underneath. The one I swear by is a Podium Pad from 2004 which was discontinued long ago -- but there are many alternatives. If you keep your laptop on your lap, almost any simple lap desk can help a lot, keeping the computer on a firm surface to let the fans do their work without smothering them with fabric/skin. There are also active cooling pads with fans in them, some of which are very well-reviewed.

Finally, I'm not sure what you're recording, but you could try using a directional USB microphone to eliminate extraneous noise from your recording environment. There are many excellent options on Amazon for under $100 (be sure it is Mac-compatible before purchasing).

The examples you've used in your question can be explained by the use of the SSD in the MacBook Air.

In March 2014 I installed a hybrid drive (what Apple calls a 'Fusion' drive) into a late 2008 MacBook Pro. The results of doing this compared to the standard HDD that was installed previously were significant!

Now, remember this was just a hybrid drive NOT an SSD. My tests showed that:

• bootup time was 16 seconds faster
• login time was 6 seconds faster
• launching MS Word was 17 seconds faster

I then tested this against a mid-2011 iMac with a traditional 7200rpm drive and the MacBook Pro was faster! Remember again this was just a hybrid drive NOT an SSD in the MacBook Pro.

One thing you should notice on the iMac though is that the first time you launch an application after booting up it will take longer than subsequent launches (unless you've rebooted again).

So yes, the SSD will explain the difference in the examples you gave, but there will be other tasks that your iMac will perform faster because they rely more on processing power rather than disk read/write times.

Whether you should install an SSD is a matter for you. It'll improve speed generally, but how much will depend on what you use your iMac for.

[EDIT]

I found the full results of my testing for the hybrid drive in my late 2008 MacBook Pro. See the table below:

As you can see, the response times also improved by doing a reformat and clean install on the original HDD. However, since you've got a late 2015 iMac I don't imagine you've had enough time to weigh the system down with unnecessary software etc.

The point I guess I'm trying to make is that the answer to your question Is the HDD/SSD the main cause of this? is yes for the examples you gave, but if you have other real life examples that would be good for some context.