I only do server work, so what I can do for you is optimize the database through mysql itself, then tune mysql for maximum caching and performance according to your server's available memory.
Relevant Skills and Experience
I run a web hosting service, work full time here and have extensive server optimization experience.
Proposed Milestones
R$30 BRL - New employer to Freelancer - Full account setup milestone.
R$270 BRL - Mysql and PHP optimized. Database optimized through mysql.
Bid includes optimizing PHP (opcache) and installing Redis for extra speed, if you have enough ram.