Hello Linux Geeksters. As you may know, Canonical intends to use either Kernel 3.19 or Kernel 20 on the final version of Ubuntu 15.04 Vivid Vervet, depending on how fast Linus moves with the kernel development.
While Kernel 3.18.2 is used on the stable branch of Ubuntu 15.04, the Ubuntu developers are planning to implement Kernel 3.19 RC5 on the unstable branch soon.
For now, only Kernel 3.19 RC6 has been released and the final version may become available in two weeks. After the release of Kernel 3.19, the development of Kernel 3.20 starts, and the stable version of Kernel 3.20 will have another 7-8 RC versions until it gets released.