Next.js 15 Performance Enhancements

In this section, we'll explore the key performance enhancements introduced in Next.js 15 and how they can benefit your applications.

Turbopack

Turbopack is a new Rust-based bundler for JavaScript and TypeScript applications, designed to be a drop-in replacement for Webpack. It offers significant performance improvements, including faster builds and hot module replacement (HMR). By leveraging Turbopack, you can expect reduced build times and a more efficient development experience. It is integrated into Next.js, offering zero-config CSS, React, and TypeScript support.

• Up to 76.7% faster server startup in development environments
• 53.3% faster local server startup times
• Up to 96.3% faster code updates with Hot Module Replacement (HMR) Fast Refresh
• Reduced memory usage during development
• Persistent caching planned for future releases to reuse compiled code across restarts
• Incremental computation that caches results down to the function level
• Lazy bundling that only processes requested code
• Unified graph architecture supporting multiple output environments
• Granular recomputing that scales with change size, not application size
• Consistent compile times with minimal variance

To enable Turbopack in your Next.js project, add the --turbopack flag to the dev and build scripts in your package.json file:

{
  "scripts": {
    "dev": "next dev --turbopack",
    "build": "next build --turbopack",
    "start": "next start"
  }
}

To enable Turbopack in your development environment:

1. Install the necessary dependencies:

   npm install --save-dev turbopack
   

2. Update your next.config.js file:

   const { withTurbopack } = require('next-turbopack');
   
   module.exports = withTurbopack({
     // Your Next.js config options
   });
   

3. Start your development server:

   npm run dev
   

Build Performance :

As of Next.js 15.4, production builds with Turbopack (next build --turbopack) now pass 100% of integration tests, with beta support arriving in Next.js 15.5.

This marks a crucial milestone toward making Turbopack stable for production use.

Support For React 19

Next.js 15 includes support for React 19, which brings several new features and improvements to the framework.

This includes

• enhancements to server-side rendering (SSR)
• improved data fetching capabilities
• better support for concurrent rendering.

By leveraging these new features, you can build more efficient and responsive applications with Next.js.

I have written articles on how you can use the latest features of React 19:

• Handling form actions using useActionState hook

Metadata API

The new Metadata API in Next.js 15 allows developers to define metadata for their pages more easily. This includes support for dynamic metadata, which can be generated at runtime based on the content of the page. By using the Metadata API, you can improve the SEO and performance of your applications by ensuring that the right metadata is always served to the client.

It looks something like this :

import type { Metadata } from "next";

// in layout.tsx
export const metadata: Metadata = {
  title: {
    absolute: "Sujay Kundu - Web Developer & Perf/UX Advocate",
    template: "%s | Sujay Kundu", // used in every page
  },
  description:
    "Sujay Kundu is a frontend engineer specializing in modern web frameworks and optimizing performance based out in Bangalore, India. ",
  keywords: [
    "web designer",
    "web developer",
    "digital experiences",
    "full stack web developer",
    "creative artist",
  ],
  authors: [{ name: "Sujay Kundu" }],
  creator: "Sujay Kundu",
  metadataBase: new URL("https://www.sujaykundu.com"),
  openGraph: {
    title: "Sujay Kundu - Web Developer & Perf/UX Advocate",
    description:
      "Sujay Kundu is a frontend engineer specializing in modern web frameworks and optimizing performance based out in Bangalore, India. ",
    url: "https://www.sujaykundu.com",
    siteName: "Sujay Kundu Portfolio",
    images: [
      {
        url: '/images/opengraph.png',
        width: 1200,
        height: 630,
        alt: 'Clover XP - Your branded LMS, Smarter and Faster'
      }
    ],
    locale: 'en_US',
    type: 'website'
    locale: "en-US",
    type: "website",
  },
  twitter: {
    card: "summary_large_image",
    creator: "@sujaykundu",
  },
  alternates: {
    canonical: "https://www.sujaykundu.com",
  },
};

And then in your pages you can use it like this, lets say in contact page :

export const metadata: Metadata = {
  title: 'Contact me'
};

So it will render 'Contact me - Sujay Kundu' in contact page

Summary

Performance Impact

The combined improvements in Next.js 15 deliver measurable performance gains:

• Development Speed: Turbopack provides up to 95% faster code updates and 75% faster server startup
• Build Performance: Improved build times and more efficient compilation processes