The minimum (fastest) spawn rate under normal conditions is 60, and the maximum spawns is 15. The modifiers from Water Candle and Battle Potion are set before these limits are checked. Invasion events (including Goblin Army, Frost Legion, and Pirate Invasion and Martian Madness) and moon Events(Lunar Event/Pumpkin Moon/Frost Moon) are a special case; they ignore any modifiers or limits to the spawning rates or number of spawns (including water candles/ battle potions).