If you don't have better ideas for improving your packet size at least push your JSON through msgpack. Using strings as keys (properties) is ultra bad for your bandwidth too. In general JSON is only suitable for turn based games.
[1] https://redka.games [2] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...
I'm about to change over to msgpack for my own multiplayer real time browser game. I'd use protobuf, but the extra code generation step would get in the way of my plans to turn my MMO into an MMO-game-as-lambdas PaaS project.
Right now, I'm using my own protocol which uses something somewhat like base-85 for encoding, except it's base-92. It's a binary packing format, but packs directly into base-92 encoding. This packed base-92 is encapsulated into JSON, which minimizes the use of keys. This might all sound horrible, but I'm able to achieve what Flatpack achieves: no copies are needed to extract the data. That, and the remaining slight JSON overhead makes it easier to debug network traffic.
Nevertheless, bandwidth-wise it could make sense anyway, but I think it makes sense to consult some benchmarks in this case.