I remember some time ago, on KX Studio, the power plan always came back to "powersave" after several minutes of playing, without any action from me.

Even the right power plans?

One thing to note is that Linux Mint (and possibly other distributions) typically come defaulting to the "powersave" mode and without any obvious way to change that.  The control panel "power management" window does not provide a way to directly change these.  So by default Pianoteq on Linux will run under "powersave" (not Modartt's fault) and this can cause clicking and audio drop-outs and glitches !

"Powersave" and "Performance" are power management modes directly linked to the Intel CPU's power management model.

To add this ability using the Mate desktop you need to go into "Control Panel" and select "Startup Applications".  From there look for the "CPU Frequency Scaling Indicator" and make sure it's selected to startup automatically.  Using that widget you can switch between "power" and "performance" at will.  For Pianoteq you want "performance" to avoid clicks and similar audio issues.

It may be necessary to install this widget using Synaptic.  If that happens you want to install a thing called "indicator-cpufreq".

You may need to restart to get that up and running (can't recall exactly what I did at the time).

After that you'll have a small indicator on your desktop panel that you can switch between different power management modes.

Why Linux Mint Mate comes without this installed and operating by default I don't know, but it's a darn silly thing to leave out as it prevents Linux users getting max performance from their systems.  In theory "powersave" should ramp up performance as required, but the problem is that in practice this leads to variable performance which causes issues.

Is not really necessary to use a specialized Linux distribution for audio, the relevant parts are in all Linux kernels for some time now.

Even the right power plans?

Use the accepted answer in the second link in sjgcit's post. That's what I did and it fixed the problem for me. It's the low-impact upgrade you are looking for.

https://askubuntu.com/questions/575505/...this-error

I'm running a later version of Linux Mint that you, but a quick search on an the AskUbuntu.com forum found some answers that may help you.  Linux Mint 17.3 is based on Ubuntu 14.04.

Short version : you (probably) need to do some updates.  Updates keep the libraries up to date and are very important for security.

Long versions are explained on these pages.

https://askubuntu.com/questions/466651/...-on-ubuntu

https://askubuntu.com/questions/575505/...this-error

You need to update libstdc++6 and gcc and g++ (at least).  Try that using either Software Center or Synaptic on the desktop.  If you have the Update Manager running it may even have a load of updates that need to be done and could be sitting on the menubar at the bottom of the screen with an icon shaped like a shield with either a green correct mark or an "i" in a blue circle - the blue circle and "i" tells you updates are available.

LibraZIK-2 is rock solid.
https://librazik.tuxfamily.org/

And of course runs Pianoteq without any problem.

My pianoteq Stage 6.3 version doesn't run in standalone but in a plug-in version it does.
When I run in a terminal I got this:

./Pianoteq 6 STAGE: /usr/lib/x86_64-linux-gnu/libstdc++.so.6: version `CXXABI_1.3.8' not found (required by ./Pianoteq 6 STAGE)
./Pianoteq 6 STAGE: /usr/lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.20' not found (required by ./Pianoteq 6 STAGE)

I don't want to upgrade all the dist, can I only install a few things to fix it?
Thank you!