First you can try disabling animations, i.e., setting the animation speed to ‘Instant’ (System Settings → Workspace Behavior → Animation Speed). Then the launcher will appear much quicker when you press ‘Start’ / the ‘Meta’ key.

Then you can try disabling some search plugins. To the right of the search field in the launcher, there’s a settings icon. Click on it and then on the ‘Configure Enabled Search Plugins…’ button. (The name of the button is misleading; you can also disable plugins here.) A good strategy is to first disable all plugins and see if this helps. If it does, enable each plugin you need, one by one, until the search becomes slow again.

The ‘Help → About KDE → Report Bugs or Wishes’ dialog available in most KDE applications ends with this paragraph:

If you have a suggestion for improvement then you are welcome to use the bug tracking system to register your wish. Make sure you use the severity called “Wishlist”.

There are videos of the talks at YouTube, but with very low video and audio quality. I think better-quality videos will follow.