If it’s spinning too slowly you have three major ways to speed it up.
Increase the force, aka add more candles. This is a bit problematic due to fire risk. Use caution.
Reduce friction. You could make or use premade bearings to make the rotation much smoother. You could use a wax to make the points that do rub slipperier. Sanding the dowel smooth might help. Sharpening the end of the dowel where it contacts the bottom might help.
Reduce mass of the blades. Rotational inertia and momentum are increased with extra mass. Use a thinner material (1/16” non PG hardwood maybe?) to make your entire assembly less massive. Bonus: this will reduce friction too. Caution: thinner material is likely to have lower thermal mass, and has greater surface to volume ratio so the risk of fire will go up.
Also:
Changing shape of the blades might also reduce the mass without losing much rotational power. They can be thinner at their base where not as much heat is reaching them.
More thinner blades will give you a more consistent rotational force.