Here's a video guide on how to do all 15 levels, as explaining it would take far too long.
One thing to note though is I made a design on level 8 that worked for 9, 10, 11, and 15. There were slight modifications for 10, 11, and 15, but this design effectively worked on 5 levels, and likely would have on earlier levels. Definitely something worth checking out!
Starting campaign - 00:00
Mission 1 - 00:17
Mission 2 - 00:33
Mission 3 - 00:51
Mission 4 - 01:17
Mission 5 - 02:21
Mission 6 - 03:19
Mission 7 - 04:04
Mission 8 - 04:38
Mission 9 - 05:33
Mission 10 - 05:48
Mission 11 - 06:27
Mission 12 - 06:40
Mission 13 - 07:27
Mission 14 - 08:47
Mission 15 - 09:10