Arduino Pro Mini slower than Arduino Nano?

The last days I tried to get a TFT-display via SPI working on an Arduino Pro Mini. After several times of trying and failing, I decided to test it with an Arduino Nano. On the Nano it worked. The program I tried was the “graphicstest”-example from the Adafruit-ST7735-library, where I changed absolutely nothing. After measuring with my oscilloscope, I found out, that the Pro Mini is much slower than the Nano. Both were running on 5V and 16 Mhz with the same program, which was the “graphicstest”. The voltage that powers both is coming from the same device. The blue signal is the signal from the Nano, the yellow one is from the Pro Mini. After switching on the voltage, you can clearly see on the diagram that the signals generated from the Nano are starting much earlier. Also, they are not lasting as long as the signals from the Pro Mini. If you zoom in, you can also see that the “single” pulses are much longer on the Pro Mini. For example: the first single pulse from the Nano lasts 8uS, the first single pulse from the Pro Mini lasts 13uS. Both are from china. Both have the Atmega 328p on board. The pin I used in this picture for my measurements is the pin 10 on both devices. This is the Chip-Select-pin on the TFT-display. The display was wired correctly. Why does it behave like this? And how can I change this, because I need the Pro Mini. The URL to the diagram is:

Verify that the resonator really is 16MHz, and the system clock prescaler (CLKPR) is set to 1:1.

How much longer? 8 times? 2 times?

I see no picture.