To Reproduce

After upgrading our app dependencies for next.js from v15.3.5 to v15.4.2 our build times increased by a factor of 10 suddenly:

Packages:

next
@next/bundle-analyzer
eslint-config-next

Build Time Before (v15.3.5):

> next build

   ▲ Next.js 15.3.5
   - Environments: .env.local

   Creating an optimized production build ...
 ✓ Compiled successfully in 72s

Build Time After (v15.4.2):

> next build
   ▲ Next.js 15.4.2
   - Environments: .env.local
   - Experiments (use with caution):
     ✓ taint
     · serverActions
     · optimizePackageImports

   Creating an optimized production build ...
 ✓ Compiled successfully in 7.8min

Any idea what could cause this? Building went from 72 seconds to almost 8 minutes :(
Downgrading results in faster build times again.

Current vs. Expected behavior

Build times should be mostly similar

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Thu, 17 Jul 2025 21:05:29 +0000
  Available memory (MB): 31923
  Available CPU cores: 4
Binaries:
  Node: 22.17.1
  npm: 10.9.2
  Yarn: N/A
  pnpm: 8.15.3
Relevant Packages:
  next: 15.4.2 // Latest available version is detected (15.4.2).
  eslint-config-next: 15.4.2
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: N/A

Which area(s) are affected?

Turbopack

Which stage(s) are affected?

next build (local)

Additional context

We tried deleting the typical folders which can cause problems after an update: node_modules, .next and .swc but no luck so far.
Disabling the experimental options taint, serverActions and optimizePackageImports did not help either.