You can configure the UART for speeds way beyond 115200 if you want. I've done DMX512 which runs at 250kbaud for example.

But, as Richard mentions, thats only half of the equation.
At the receiving end you need to be able to both A) store the incoming bytes at that high pace and B) process the data.

Is the data a continous stream or short bursts with relatively long "silence" in between?