A slow store cannot be diagnosed from one PageSpeed score. Measure the home page, a category and a product page separately, then compare a first visit with a repeat visit under the same test conditions.
Find the real bottleneck
Check server response time, render-blocking resources, image sizes and JavaScript work. Review the supported PHP version, active modules and database load. Fix the measured cause first: compressing an image will not repair a slow SQL query.
Where page caching helps
Full-page caching reuses eligible public HTML and can reduce repeated PHP work on home, category and product pages. Cart, account, checkout and personalized content must bypass the public cache. Test price, stock and checkout after a change. Public page caching does not automatically speed up the back office.
Explore the PrestaShop cache module and its requirements
Source : PrestaShop Help Center.
Cold cache, warm cache and PageSpeed Insights
Compare several mobile runs on the same URL, checking server response, LCP, CLS and Speed Index. Distinguish initial page generation from warm-cache delivery. Heavy images or third-party scripts can remain slow after caching is enabled. Do not draw conclusions from a single PageSpeed score.
If the back office is slow rather than the public shop, use our guide to diagnosing a slow PrestaShop admin: the causes and tests are different.