We have LimeSurvey 2.06 (Build 160129). We have several live surveys running at present.
Our current setup is:
PHP Version => 5.5.31
My SQL Version: 5.5.49-cll

We want to upgrade PHP to 5.5.9 and MySQL to 5.7. We need to do this because another software
we want to install on the same server requires these versions.

If we upgrade to newer versions of PHP and MySQL will it cause any problems?
We don't want the live surveys to be affected in any way.
How should we proceed?

Thanks.

Hmmm, I might be wrong, but the PHP Version you want to "upgrade to" is actually a downgrade. 5.5.31 > 5.5.9.

I,

LimeSurvey is fully compatible with PHP5.4 to PHP5.6.
Not a lot user on PHP7 but have some.

Thank you DenisChenu and holch.