The one lightweight alternative that I didn't see mentioned above is vim with the Vim-LaTeX plugin. I've heard of, but haven't actually used it. I have edited LaTeX with just vim - not as user friendly as a complete IDE, but effective in an emergency.
The site for the plugin is at:
Another alternative, if you already like kile, may be to see if you can improve the performance by tweaking the graphics settings. There are some nasty performance issues with certain KDE applications, particularly when running them on systems with the proprietary NVIDIA drivers. I have a xeon based workstation with a relatively high end NVIDIA card where the performance of kile was extremely poor, while an older, lower powered system with integrated AMD graphics didn't have any issues. In my case, switching kile to use raster graphics solved most of the performance problems. Try starting kile with the command:
kile --graphicssystem raster
If that helps, you can append the "--graphicssystem raster" to the exec line of the kile.desktop file.