Optimization of php code 7.2

Hello, our project is in php and 7.2, we need an optimization code that was much less load on the server and the database. Just need to optimize the PHP files 18 pieces (will give 2 of the file to optimize the access to test server will provide in podobnosti).

PS to superfluous questions did not arise: the database Itself is already optimized SQL programmer with 12 years of experience, the server itself optimized sysadmin with 10 years of experience.