How do we improve site speed without rebuilding the whole storefront?

Performance work has a reliable order of operations, and skipping to a rebuild usually means the same problems reappear on new code.

Work in this order

1. Measure with field data — real user monitoring, not a single lab score on a fast connection.
2. Images — correct formats, correct dimensions, lazy loading below the fold. Usually the single biggest win.
3. Third-party scripts — audit every tag. Most sites carry several nobody can account for.
4. Render-blocking CSS and JS — defer what is not needed for first paint.
5. Server and cache — full-page caching, query optimisation, and a CDN configured for your catalog.

Set a target that means something

Pick a threshold tied to revenue rather than a score out of a hundred, and track it per template — category pages, product pages and checkout behave very differently and average badly.