@Matteo It depends on what modules you're using. As far as I know, the crashing issue is only when showing a matplotlib plot in Python 2.7. I haven't heard of any other crashes or major issues on Python 2.7 only. But I can totally understand that you don't want to upgrade in this situation, especially because it's almost impossible to downgrade iOS apps to an older version.
In any case, I would recommend looking into Python 3 at some point. Python 2 will no longer be supported after 2020 (the exact end of support date is not decided yet), and many libraries will stop supporting Python 2 around that time. Of course this doesn't affect any of your existing code, Python 2 won't break after 2020, but you won't get any updates and can't use most new code.
If you have some short scripts that aren't very complex, you can try running them on Python 3, and see if you run into any problems. Many common Python-2-to-3 problems are trivial to fix (adding parentheses to prints, updating uses of functions and modules that were renamed, etc.). The "Python 2 to 3" editor action can help with that, but I would recommend making a backup of your code first - automatic translation is never perfect.