Hey, I'm using Kubuntu 15.04 on my main PC and my current kernel is:
3.19.0-26-generic

Should I update to the latest kernel ?
https://www.kernel.org/
Or should I trust my distro and let it decide when it will update my kernel ?

If I update, what are the chances it will break my system ?
and if it does, what should I do ?

You should see if the distribution update tools have available a kernel upgrade versus not. Especially for Kubuntu. Many full desktop type distributions customize the kernel from the standard to work more in tune with the distribution. Nothing wrong with that, just customizations though and if you just grab the standard kernel with a default configuration you stand to lose some functionality or even not have the system run properly. Ubuntu and derivatives are no exception here, chances are they have customize the kernel.

I personally wouldn't upgrade but install the new one additionally : you will be able to boot with the new one and fallback to the known working one if something appears to be broken.

Seeing what @rtmistler answered, I would suggest you build last kernel using at least the config of the one you actually run as a base.

ok, thank to you both :3

I've actually been experimenting with this lately. I was able to take the latest Vivid kernel (4.0) and install it sucessfully on Debian 8.1, Ubuntu 14.04, and (of course) Ubuntu 15.04. As far as I can tell the Ubuntu kernel works flawlessly, although I haven't done anything extensive.

I did notice that Debian boots much faster with the Ubuntu kernel, other than that everything seems normal.

Going to try with Ubuntu 12.04 and 10.04, I have a hunch it will work. Also want to try this with RedHat based distros like Fedora and CentOS (and possibly Mandrake if I can get away with it.)

What I found is that Ubuntu doesn't push the latest kernel in standard updates (probably for compatibility and ease of troubleshooting), but the latest kernel is indeed available officially from Ubuntu. I imagine Fedora has something similar, only through the standard repos.

I wouldn't bother compiling your own kernel unless you can't get one specifically for your distro.

If I update my kernel to the latest version, would I continue to get updates for other parts of the system through the update system of my distribution (Mint 17.2) ? I'm assuming that some of the updates might not be compatible with the new kernel.

I don't see why not. If a newer kernel comes out, you'll likely get the update.

Oh, and I did get around to trying kernel 4.0 in Ubuntu 10.04...seems to have broken X somewhat though.

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I followed the instructions found in the following 'for fun'... No harm to try! :

http://www.cyberciti.biz/faq/debian-...-linux-kernel/

The 4.2 Kernel actually came up and ran on my LUbuntu system without errors! However it has at least one major flaw. Anything text, whether shortcut names, terminal text, FireFox, LibreOffice documents, etc. will have a few missing characters or junk characters. Not sure where to look. Went back to the original 3.19 kernel and all is well. Wonder if Nvidia Video compatibility problem, or what. Haven't a clue where to start looking.

Revisiting this as I found what is causing the problem I had with missing characters. Turns out to be anti-aliasing.

I got back on this project as I 'upgraded' to LUbuntu 15.10 the other day. Guess what.... The problem surfaced again with the 4.0 kernel that was part of the upgrade. In other words there was nothing wrong with my kernel build! So did some research and found some references to anti-aliasing. So turned that off and no more problem.... Wahoo... But the text of course looked blocky and not so smooth. However I could read it just fine now! Next I loaded the Nvidia proprietary drivers and re-enabled anti-aliasing and all is well. Faster too. So the only conclusion is there is a problem with anti-aliasing with the stock nvidia driver that the 4.X kernel loads by default.

Thought I'd pass along....

My vidio card is an Nvidia 750.

Anything having to do with GUIs or visual display would not be a "kernel" issue: they would be an issue with XWindows/XOrg.

(I can't speak knowledgeably as to whether these systems have any kernel dependencies.)

Oh, I think it is. The previous 3.19 kernel never had a problem. It was going to the 4.2 Kernel that the problem surfaced for me. I thought it might be me because building a kernel can introduce some funny problems... until the newest distribution LUBuntu 15.10 came out with the same kernel (they built) exhibited the same problem after the upgrade. So it 'appears' anyway the problem has to be something to do with the kernel. There is a stock Nouveau kernel driver involved. And bypassing it, by going to the proprietary Nvidia driver fixed (masked?) the problem.