Our checkout page was slow on mid-range Android phones, which is most of our users. What actually moved the…

Our checkout page was slow on mid-range Android phones, which is most of our users. What actually moved the needle: 1. Moved payment SDK loading after first paint (was blocking: 900 ms) 2. Server-rendered the cart summary instead of fetching on the client 3. Replaced a 180 KB date library with Intl APIs 4. Preloaded the hero font and set font-display: swap 5. Dropped a carousel nobody used (analytics said 0.4% interaction) Conversion went up 6%. Biggest lesson: measure on a real ₹10k Android phone, not your MacBook.