I don't particularly like this article but it suggests acoustic data rates are around 1kb/s
Since the OP is looking for a maximum of 2kb/s this may not be a problem, but it is kind of strange to specify a maximum. If the OP really wants a minimum of 2kb/s then actual data rates and cost of achieving it in commercial systems would definitely be worth exploring.
Maybe the OP will always be in clear water but if that is not certain then communicating by light is a bad idea.
A target distance of 15m sounds achievable. Waterproofing will be a problem, a ball at 30m depth would be crushed to 1/4 of its surface volume.