2N2222A is a high speed device, so yes, as a device its a good choice - as a transistor (low collector to base or ground capacitance).
The speed "factor" will be dependant on the value of the collector load. If you have "open collector" set up, that means the load is at the far end, where a pull-up resistor will pull the Tx line high when the 2N2222A turns off. Just how fast this returns to the high state depends on the Tx line length, or more accurately, the capacitance it has (intrinsic) to ground. You can get an estimate if you know the capacitance (roughly). If the pull up is 1K , and the capacitance is say 100 pF, the time constant from this RC combination is R times C seconds, or 10e3 times 10e-10 = 10e-7 seconds. That would indicate a speed of 10 MHz, but generally speaking, you should allow five time constants rise time, so that brings it down to about 2 MHz.
A smaller pull-up load resistor (470R) would pull it up faster, but more current has to be switched on and off. Its usually a compromise.
Better than a single transistor (pulling down) is a LINE DRIVER, which has a totem pole output - that means a complementary PNP transistor pulling upwards at the send end, rather than relying on the load resistor alone to pull the line high. But that's more complex and not a simple "open setup".