The goblins solve the puzzle of the carrot patch and proceed to the rat's den.
How to Clear Gobliiins Level 15
Switch to 
Bobo/Asgard and change the cursor to a fist, and
click the cannon to tilt it up. Then have him punch the pile of cannonballs
in the bottom-right of the screen to make one fall off. Switch to
Dwayne/Oups and change the cursor to an open hand, and pick up
the cannonball that fell, then switch the cursor to a fist and click the
cannon to put the cannonball in.
Then have Bobo/Asgard punch the cannon to make it tilt
upward again.
Next, have Dwayne/Oups click the small box in the upper-right
of the screen to get matches. Change the cursor to a fist and click the
cannon to light it. A carrot will fall from above.
Have Dwayne/Oups pick up the carrot and click the cannon
to throw it in.
Have Bobo/Asgard punch the cannon to make it
horizontal.
Then have Dwayne/Oups pick up the matches. Have him
use the matches on the cauldron in the bottom-left of the screen.
Then have him use the matches on the cannon.
The carrot will go flying into the cauldron. If the fire is not lit under the
cauldron, have Dwayne/Oups use the matches on the cauldron.
Eventually, Shadwin will wake up from the smell.
Make another carrot fall from the ceiling (the instructions are in the
first and second paragraphs on this page). Then have 
Hooter/Ignatius
use magic on the carrot to turn it into an ear trumpet. Have
Dwayne/Oups pick it up, then change the cursor into a fist
and click Shadwin, who is sitting awake in the chair. (If he's asleep,
follow the instructions in the previous paragraph.)
A mallet will appear on the ground. Have Dwayne/Oups pick it up,
then change the cursor to a fist and click the gong. The gong will open up,
and an object will appear on the upper walkway. Go pick it up to get a
pendulum.
This completes the level. Click the flashing "Go" in the gong. Make a note of the code in the bottom-left of the screen ( ), then click anywhere to continue to the next level, The Giant Floating Statue.