Originally posted by Cap'n Bells:

you make a strong point +1 however there is this line in the wiki
line ONE " If an event is already running when a new one triggers, the previous event will automatically end."

That's easy to explain.
If you leave the area where a raid is currently active, the raid is paused and will only resume when you go back in that area.
If, while that raid is paused, the check for raid starts a new raid on your current location, the previous, paused raid is canceled.

Originally posted by Cap'n Bells:

how does it trigger? when a event/raid is already running?
line TWO from wiki " The source of death for a creature is not tracked. Therefore, despite a player's best efforts to not kill a certain creature to avoid certain events, the environment (e.g. a Surtling walking into water) or a neighboring biome (Lox fighting a Troll) can unlock those events for that world."
so consecutive events can trigger from actions other than boss kills, ..are they on same timer... clearly not if you read line ONE
i still surmise the chance is NOT zero

Not quite. Event triggers and raid checks are two different things.

An event trigger adds the relevant raid to the list of possible raids.
A raid check rolls for the possibility of starting a raid from the list of possible raids.

Whatever happens, there is only one check for raid every 46 minutes (I should have checked the wiki yesterday, it's not 45 minutes). That number is fixed, which makes it impossible for 15 raids to happen in only 6 hours.

Edit: The more I think about it, the more it feels like very old-school D&D random encounters. I like that.