Why We Migrated to Next.js 15 (App Router) — And What You Should Know

"If it works, why change it?"

That's a question I get a lot when working on large production systems. But here's the truth: sticking with "good enough" can sometimes hold your platform back.

In a recent project, we decided to migrate a mature digital customer platform to Next.js 15, using the new App Router. It wasn't just a tech refresh—it was a strategic decision based on performance, scalability, and long-term maintainability.

Here's what we learned.

The Context

The platform served thousands of users daily, and while it was working well on Next.js 12, we were starting to feel the weight of legacy patterns:

Pages were growing bloated and tightly coupled
Developer onboarding was getting slower
SSR and SEO optimizations were getting harder to maintain

This wasn't a greenfield app. We had to plan carefully, test aggressively, and make sure everything continued to work flawlessly.

Why Next.js 15

Next.js 15's App Router introduces a more modern, modular approach to building applications:

Layouts and nested routing feel more intuitive and flexible
Server Components reduce client-side JavaScript and improve performance
Streaming, loading states, and React Suspense are first-class citizens
Colocation of data and views simplifies mental overhead

As a team already invested in clean architecture and performance-driven development, this felt like a natural evolution.

How We Approached the Migration

We took an incremental route:

Kept Pages Router for parts of the app still under migration
Rebuilt core routes using the App Router to test performance and maintainability
Refactored shared UI components to be compatible with Server Components
Moved data fetching logic into async React components
Improved CI/CD workflows to support partial deploys and better caching

We also maintained high test coverage and used performance budgets to track improvements.

What Changed

The migration wasn't just about new tech—it actually changed how we worked:

Developer experience improved. We shipped faster and with fewer bugs.
Performance metrics got better. We saw noticeable improvements in load times and SEO rankings.
Code was easier to scale. Modular routing and layouts allowed us to build without creating tech debt.
We stopped over-engineering. Server Components let us remove unnecessary Redux or data fetchers from the client side.

What Was Hard

It wasn't all smooth sailing:

Documentation was still evolving, especially around edge cases with middleware or third-party libraries.
Some community packages weren't ready for the App Router model.
Our build pipeline needed tuning—build times increased initially due to extra complexity.
The learning curve required knowledge-sharing and pairing sessions across the team.

But these were short-term hurdles. Long term, the benefits far outweighed the pains.

Key Takeaways

If you're considering migrating to Next.js 15, here's what I'd recommend:

Audit your app. Know where your routing, data, and state management live.
Don't rush. Migrate incrementally and track progress.
Lean into React Server Components, but test early and often.
Monitor user experience. Don't optimize for dev happiness at the cost of performance.
Make it a team investment. Migration is both a technical and a cultural shift.

Final Thoughts

Migrating to Next.js 15 gave us a better foundation to grow the platform, serve users faster, and code with more confidence. It wasn't just an upgrade—it was a step toward building software that scales with purpose.

If you're working on a large SaaS product or managing a team trying to modernize your frontend, I'd say now is a great time to explore this new direction.

Want to connect or talk architecture? Reach out on LinkedIn or just drop me a message.