Troubleshooting and Performance Optimizing Magento 2

We are running a Magento 2 Shop on a deticated Ubuntu Server with Plesk and need support to fix a serious performance issue. We have 13 store views and the server is setup with 2 IP addresses that are assigned to selected store views. Apply for this project only if:
- you have extensive experience with Magento 2 on Plesk servers
- you know exactly what you are doing
- you can start right now