Magento 2 CE – Memory Limit Reached When Saving Product

You can try to increase de memory limit of your php:

Open /etc/php5/apache2/php.ini in a text editor

Change memory_limit to:

memory_limit = 256M

And you can check creating a file info.php

<?php phpinfo(); ?>

Check the variable: memory limit

The official system requirements (or rather: recommendations) are:

Increase the PHP memory limit to at least 768MB for normal operation or 2GB for testing.

^{Source: Recommendations for CentOS and Ubuntu}

I would only increase it to a higher value if you encounter problems where the memory limit is hit. Then debug and fix these problems, and set the memory limit back to normal when successful.