I think if you go only for this fireworks, you don't need go because only 15minutes and if you watch at merikenpark, maybe crowded. However, you go also other spots, it is worth to going because no charge and you can see fireworks near the launch location. It is enough to go merikenpark about 17:00-17:30 or 17:45 for get good location. I think this fireworks is not main but good sub content for your trip.