The project isn't huge, but it is on the larger side. It contains about 1.5 million lines of PHP code across 5400 files, though that number hasn't significantly changed recently.
It is based on Zend Framework 3: https://framework.zend.com/learn - this framework has since been rebranded to Laminas but we have not made the change on our end yet.
One possible issue is the amount of vendor code, our vendor folder contains 11,000 php files. Again, this hasn't changed recently.
I am the only one of my team that uses PHPTools, most of my colleagues use PHPStorm and have no issues with the size of the project. I didn't either until very recently.
Is there anything else I can look into?