Are you downloading this file: IoT Download - Linux* Development Kit ?
Also, could you post a screenshot of when you get the error message?
On Ubuntu 15.10, are you doing the following?
- Download the file
- Extract the files from the iotdk-ide-linux.tar.bz2
- Open a new Terminal Session
- Go to the folder where are the extracted files
- Run cd iotdk-ide-linux
- Run ./devkit-launcher
As mhahn said, which java version do you have in your machine?