Python 3.15 is still in development. This release, 3.15.0b3, is the third of four planned beta releases, containing around 195 bugfixes, build improvements and documentation changes from 86 contributors since 3.15.0b2.
Beta release previews are intended to give the wider community the opportunity to test new features and bug fixes and to prepare their projects to support the new feature release.
See the official website.