Unfortunately, there aren't many ways to speed up Unity, the main thing is closing out every other program open. Even Google Chrome can be a surprisingly large CPU drain. From there, less complicated, and less total objects you have in a given scene can help speed up the development stages. Sometimes "muting" your object can help alleviate the processor speeds.
The unfortunate part of all of this is that once you get to the stage of recording your walkthrough, you'll obviously need these objects to be visible. At that point, you'll just want to make sure every other running process is terminated. If you've followed all of these tips and are still having difficulty recording a walkthrough of your scene, get in touch with the learning lab at help.learninglab.xyz