Use arduino nano to upload sketch to pro mini without USB to TTL converter.

RX-RX, TX-TX, 5v(3v3)-Vcc, Gnd-Gnd
Set reset pin on Nano to Gnd.
In IDE set board "Arduino Pro or Pro Mini (5V, 16 MHz) w/ ATmega328", and COM port Nano.
NOTE:- don't forget to press reset button on arduino pro mini just before uploading code.