I recently installed magic lantern on Canon 500D, but now it responds much more slowly than it used to. Is there a way to improve this?
It is a simple fact that Canon cameras with Magic Lantern installed have a slower start-up time. There is nothing you can do to improve the start-up time.
Magic Lantern is a 3rd party software for Canon Cameras. Because of this, all the software builds are experimental and sometimes unstable. This can make it very hard to diagnose why it "responds more slowly than usual".
To try and fix the responsiveness issues I would try the following: 1. Completly restore the Camera using the original firmware and then reinstall Magic Lantern. 2. Format all your cards that Run Magic Lantern and then Reinstall Magic Lantern on to them. 3. You can always try a new 'Nightly Build' it might fix things for your camera. 4. You could always install an earlier build of Magic Lantern that is known to work. Personally I only run the Stable Builds on my Canon 50D. 5. Finally this is a long shot but you could try using a faster card in your camera.
Hope one of these methods works for you!