8.15 was just branched:
https://github.com/libvips/libvips/tree/8.15

Website updated in this branch:
https://github.com/libvips/libvips/tree/gh-pages-8.15

Release notes here:
https://www.libvips.org/2023/10/10/What's-new-in-8.15.html

TODO:

• Propose v8.15.0-rc1 - v8.15.0-rc1 release proposal #3719
  • Update libvips/build-win64-mxe for -rc1 - https://github.com/libvips/build-win64-mxe/releases/tag/v8.15.0-rc1
  • Open PR at lovell/sharp-libvips for -rc1 - Upgrade to libvips v8.15.0-rc1 lovell/sharp-libvips#198
• Test and update downstream bindings.
  kleisauke/net-vips@master...vips-8.15
  kleisauke/wasm-vips@master...vips-8.15