I don't have an answer on if there's a bylaw that puts boundaries on that sort of thing. They obviously love their lawn which is their prerogative as much as that sounds like more watering than anyone I've known with a golf green lawn has needed to do.
If they’re coming onto your property and placing the sprinkler when asked not to I could see that being a problem and you’re not being unreasonable to ask them not to.
Can you elaborate on how this is effecting you or your property? Is it a wood fence on your property that you’d have a concern over the fence rotting with that much water constantly hitting it? Are there plants you grow in the ‘spray zone’ that are more sensitive to over watering than grass? Does water accumulate on your property in a way that could be a slipping hazard for you or others? If it's any of the above have you made sure they know it's having that impact?