Don't use "Every X seconds" for this. It will affect all enemies at once, which will look weird. Also, if you return to this layout, "Every 15 seconds" may start earlier than you expect.
You need Timer behavior here. Add Timer to Enemy sprite. In On Enemy created event (or on start of the layout) start a timer "attack" for 3 seconds. In On Timer "attack" event change animation and start another timer - "tired". In "tired" timer start "attack" timer again.
You can randomize the time a little to add variety to your enemies. For example, start a timer for random(3,4) seconds.