Keeping pages fast without a framework
Most pages are slow for boring reasons: oversized images, scripts that block rendering and fonts that load late. None of that needs a framework to fix.
Start with the content
Write the page as plain HTML first. If it reads well with no styling at all, everything you add afterwards is a bonus rather than a requirement.
Weigh every request
Each file a page asks for costs time, especially on mobile connections. Combine small stylesheets, compress images to the size they are actually shown at, and prefer system fonts when a custom typeface is not essential.
Measure on a poor connection
Test with throttled network settings, not only on a fast office line. If the page is usable there, it will be pleasant everywhere else.