This release corrects a bug introduced with release 3.15.1 yesterday. This caused a crash when auto-restarting (all platforms, TWS and Gateway).
If you have already installed 3.15.1, then just extract the IBC.jar and version files from the zip and overwrite your existing versions (don't forget to ensure execute permission is set on Linux and macOS).
If not then use the IBC.jar and version files from this version when you do.