In this case it might be wise to switch ground, because the TX/RX pins are permanently pulled up to 5volt.
Base resistor value is wrong.
Using transistor Hfe to calculate base current for a switch is a common beginners mistake.
This is only important when the transistor is used in it's linear region (amplifier).
When the transistor is used as a switch (collector voltage lower than base voltage),
then the base needs 5-10% of the collector current (see Ic/Ib in the saturation graph of the datasheet).
Change that 15k resistor to 1k.
Leo..