PHP 7 is the first significant version update to PHP in several years. There are several upgrades and general changes that you might be interested to know about. As always, we recommend that you use the latest software versions whenever possible. This article includes instructions for upgrading to PHP 7.
PHP 7 is much faster and, due to changes in the way errors are handled, more stable. Dynamic websites that are built using popular content management systems (CMS) like Wordpress should run more efficiently and be less likely to crash when compared to previous PHP versions.
From the official PHP documentation:
the fact that PHP 7.0 is a new major version, and efforts have been made to
make migration as painless as possible, there are still backwards
compatibility issues that you may encounter. This is less of a concern for newly provisioned servers with new sites,
but could still be an issue if you intend to migrate sites that utilize
older versions of PHP.