Next.js 15 dropped with some game-changing performance improvements and new features. But should you upgrade from Next.js 14? Let's compare them head-to-head with real benchmarks and migration guidance. Quick Comparison Table Feature Next.js 14 Next.js 15 React Version React 18 React 19 RC Turbopack Dev only (beta) Dev + Build (stable) Build Speed Baseline 2-3x faster Bundle Size Baseline 10-15% smaller Server Actions Stable Enhanced with validation Partial Prerendering Experimental Stable Caching Aggressive default Opt-in (breaking change) Async Request APIs Sync Async (breaking change) Hydration Errors Basic messages Detailed with source Image Optimization Good Better (AVIF support) Minimum Node.js 18.17 18.18 Performance Benchmarks Build Time Comparison I tested both versions on a medium-sized Next.js app (50 pages, 200 components): Next.js 14: ✓ Compiled successfully in 45.2s ✓ Linting and checking validity of types... ✓ Creating an optimized production build... ✓ Collecting page data...…