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...…