14 DAY TRIAL // Ubuntu 15.04 (Vivid Vervet) is arriving tomorrow, April 23, and it will be using a modified Linux kernel 3.19.3. The developers say that they are also preparing Linux kernel 3.19.4 and 3.19.5 for the upcoming updates.
Canonical doesn't just implement a Linux kernel into their system; they make a number of modifications to it, and that means it's actually a customized version of the stock one. They have a kernel team that is doing this sort of work, and they've been known to pick even kernels that reached end of life (EOL) during the support period for one of their distros.
Linux kernel 3.19.4 and 3.19.5 have been released already, so you're probably wondering why they haven't been adopted just yet. The answer to the question is pretty simple. The kernel team does a lot of testing, and that testing needs time. They don't just slap the latest version and go home. In this case, they might just as well add Linux kernel 4.0 and go home.
Linux kernel 3.19.3 is not an LTS release
If the version number is of any indication, the kernels with odd numbers don't become LTS versions, so it's safe to say that the same will happen for the 3.19.X branch as well. It hasn't stopped Canonical from adding it to their distro and they had no other choice. It was the most advanced release available at that time.
"Our Vivid kernel remains based on the upstream v3.19.3 stable kernel. We do not intend any additional uploads before release this Thurs. We have started to queue the v3.19.4 and v3.19.5 stable patches for our first Vivid kernel SRU," said Canonical's Joseph Salisbury.
Ubuntu 15.04 (Vivid Vervet) will land sometime tomorrow (the actual hour is not known), so users will be able to get a closer look at what Canonical has done so far.