Inky Impression screen refresh takes 2x longer than expected

I have a Inky Impression (7 colour ePaper/eInk/EPD) screen working on a Raspberry Pi Zero 2 W
In the product page noted “It takes approximately 15 seconds to refresh the display.”
however mine takes about double(29secods.)

Do I miss bus speed settings or configuration for normal speed refresh?
Any infomation is helpful, Thank you!

Reference - It seems around 15 seconds to refresh.

What I did
1.Fresh install the latest Raspberry Pi OS(bullseye)
2.Install Python library with examples - “curl | bash”
3.Reboot and run the example script.

Tested with older Raspberry Pi OS(Buster) with Raspberry Pi 4, I’ve got the same result.