Wouldn't it be easier to use the timer behaviour instead of the wait action?
scenes = 0
-- every tick
simulate pressing right
-- trigger once
start timer with tag "scenes0a" for 15 seconds
on timer "scene0a"
set maximum speed to 40
start timer "scenes0b" for 3.5 seconds
on timer "scene0b"
-- set maximum speed to 30
-- start timer "scenes0c" for 1.5 seconds
on timer "scene0c"
set maximum speed to 40
start timer "scenes1a" for 0.5 seconds
on timer "scene1a"
set scenes to 1
sprite set mirrored
etcetera..