It could be right, 30 secs was my own timings. 2 updates were taking about a minute. Although on a different brand 5.7" 7 color eink display (Waveshare) but they look the same except how they are connected

I think it might be because I think two screens are using different algorithms to change images. Mine can only do a full clear, the author mentions that you need to do full clears from time to time to avoid ghosting or permanent burning. So maybe 15 secs is only for non-full clear image change

Tbf not much difference between 15 or 30 secs when it comes to usability