Today PHP 5.5 reached its end of life.
Every PHP release has a certain amount of life after which the version is marked as security fixes only, and after some more time it's officially unsupported by the PHP group.
PHP 5.3 is out of support since 2015, while PHP 5.4 reached its end in 2015.
PHP 5.6 will stay with us until the end of 2018, just like Joomla 7.0.
Now, what does it mean to you as a Joomla and JooCommerce user?
First, if your hosting provider does not support a higher release, ping them to update the server. It's important for your security AND for the site speed.
A old PHP version probably means an old server too, so you can probably be moved to a newer server by them, with access to a newer PHP release.
If you're self-hosting the site, then it's your responsibility to update, and you should :)
Speed wise, PHP 7, fully supported by Joomla, is now running 15x PHP 5.4, and almost 2x Joomla 5.5 and 5.6, so it's very much worth an update, also considering Google values a lot the site speed.