Optimize Prestashop Speed

I need someone to optimize the speed of my Prestashop site, armtoys.bg. It is particularly slow when adding items to the cart, especially with 50 or more items, taking over 10 seconds.

Requirements:
- Optimize both front-end and back-end performance
- Improve speed of shopping cart and checkout modules

Ideal Skills and Experience:
- Proven experience with Prestashop optimization
- Strong understanding of front-end and back-end performance issues
- Familiarity with shopping cart and checkout modules
- Ability to identify and resolve specific module-related performance issues

Please provide a detailed plan and timeline for the optimization work.