Original Adafruit_ST7735 Driver is a bit outdated with deprecated functions so I updated it.
It also uses the standard SPI library which is slow, not because frequency, but because delay between writes when using RTOS.
I was trying to solve this problem for days, optimizing compilation and thread priority and I came across BurstSPI.
BurstSPI kinda eliminates the receiving delay after sending spi writes, so I adapted Adafruit library and it is blazing fast now.
Adafruit ST7735 with BurstSpi:
BurstSPI (added config for STM32F103RB )