$ uname -a
Linux namedeleted 3.14-0.bpo.2-686-pae #1 SMP Debian 3.14.15-2~bpo70+1 (2014-08-21) i686 GNU/Linux
I would suppose this means I have 3.14.15?
Your kernel version is 3.14-0.bpo.2-686-pae. I suggest you use "uname -r" to get just the real kernel version and no other output. For example, if you look in the /lib/modules/ directory , you should see a directory named "3.14-0.bpo.2-686-pae". That directory holds all of the loadable modules for your kernel.
Confusing technicality: technically "3.14-0.bpo.2-686-pae"is the "release" name and "#1 SMP Debian 3.14.15-2~bpo70+1 (2014-08-21)" is the "version" name (at least according to the uname command) but people generally use the release name when they talk about the kernel version. You should too.
It is there. It is the uppermost version "3.14" on the second page. The "-0" and what follows in your "uname -r" output does not indicate a change in the Linux source so you want the source code version "3.14". I think someone may have goofed with the "version" string when they built your kernel and that is why the confusing "3.14.15-2" shows up in the output of "uname -a". Stick with using "uname -r" to find your kernel version and your life will be easier and less confusing. If you are confused about "uname -r" versus "uname -v" (which *is* very confusing) then take a look in the /lib/modules/ directory.
When should I upgrade? How do I know when I should upgrade?
Generally, you will only need to upgrade if there is a serious security vulnerability or if you have new hardware that doesn't work with your existing kernel. Serious security vulnerabilities are rare but they do happen. They are rare enough that when one is discovered it is big news.
How knows a less interested user?
Since major security vulnerabilities are rare, the most likely tip off that a kernel upgrade is needed is that the current kernel does not work with your new hardware. My guess is that the most likely problem would be not being able to get accelerated graphics to work on a computer that has a recent Intel graphics SoC or chip. Another common problem area is a very recent wifi or network chip. Kernels will generally not have support for hardware that was released after the kernel was released. Even if the hardware is released first, there is some time lag (months?) before support for the new hardware gets added to the kernel.
Occasionally new software may require a feature that is only available in a more recent kernel but this doesn't happen often unless you use older kernels. As long as you update your system every few years and you don't try to run on the latest and greatest hardware then as a normal desktop user you should generally not have to worry about the kernel version.