I recently migrated an opencart site from a very old PHP version to a new host capable of running up to PHP 7!
The migration went fine, and the only things I needed to change were the paths in the config.php files.
After the migration the server response time has seriously degraded, from about 200/300ms to 4-5 seconds. A HUGE drop!
Troubleshooting so far
I have checked permissions on cache folders, cleared them down and Opencart successfully regenerates them, so im fairly confident this is not the cause.
I've asked the new host to see if DB connections are taking longer, they may be able to help here?
Any other suggestions or action I can take to debug? Is there any profiling in Opencart that I can enable to try find the culprit?