I have the Macbook Air 11' late 2010 with Core 2 Duo and 2 GB RAM. I decided to install XCode 7, but it requires Mac OS 10.11 El Capitan. So, should I upgrade OSX on my 5-yearold macbook air? I worry about work speed.
I'm posting this answer from a late 2010 11" MacBook Air running El Capitan, and I have no performance issues. It runs very well. But this machine has 4GB of RAM, not 2GB, and that might make a difference.
Remember that 10.6.8 has not received security updates for years now, and will be full of unpatched vulnerabilities. It is a risk to keep running it.
Here is a link to Mac's system requirements for El Capitan. http://osxdaily.com/2015/06/09/os-x-el-capitan-system-requirements-compatible-mac/
Macbook Air is listed as needing "MacBook Air (Late 2008 or newer)".
In addition, you mentioned your processor.
... the Mac must have a 64-bit CPU, which is typically an Intel Core 2 Duo or newer processor. Beyond that, the requirements are pretty soft and forgiving
Based on the system requirements released by Mac, you sound clear.
As mentioned by Mike Scott in its answer, I can confirm that doubling the RAM from 2GB to 4GB will make a very significant difference.
On a quite similar model as yours in term of performance, a MacBook white 7,1 mid-2010 with 2,4 GHz Intel Core 2 Duo (and NVIDIA GeForce 320M 250Mb GPU) that was running Snow Leopard 10.6.8, going to 4GB RAM changed the computer from very slow (almost "frozen") to very fast, even with its original old 5.4 krpm hard drive.
After upgrading to an entry-level SSD and running El Capitan on the same computer, still with 4GB RAM, I cannot observe performance issues. I cannot tell if I had kept the original hard drive, but I assume the performance would still be fair. (I assume the original HDD has a good controller.)
No - make sure you have a good backup so you can test the upgrade without losing your apps and data that matter to you most.
Yes - once you are confident in your backup, you have only time to lose and can see if things are better or worse with the later software features and security and options for newer third party apps.
And, I would probably do an erase install staying at your same version to see if that speeds things up before any upgrade, but that’s just me. Here is a very excellent thread discussing why you might chose one of these two OS - third party browser support.