To slow it down, you can either:
a) change your commands to make the turtles move slower, etc., or...
b) record repeated repeated/duplicate frames.
Choice a is probably harder, but has the possibility of making the video smoother as well as faster.
Choice b is quite easy! Everywhere in your code where you wrote
change it to
repeat 10 [ vid:record-view ]
The exported video should now be 10 times slower, since it will now show the same repeated image for 10 whole frames each time...