This is not SAMD21 data, but the following link may be helpful.
Even if you increase the SPI clock speed, the data transfer speed will not increase significantly if the interval between 1-byte transmissions is large.
If measurement is necessary, you can obtain similar data by uploading the sketch you want to try.
The SPI clock frequency of SAMD21 is 24 MHz by default, but I set 12 MHz to match the 15 MHz specification of ST7735.