And what has that do with the core developers? Is there a bug that prevents 2.1.5, but not 2.1.4 from running on Windows? The hostility against Windows is usually rather a community issue.

And they're not releasing pre-compiled versions for any other OS either. Build it yourself [1] or try to be patient until Luis Lavena uploads the Ruby Installer for 2.1.5.

[1] https://github.com/oneclick/rubyinstaller (edit config/ruby_installer.rb to compile 2.1.5 and not 2.1.4)