LP5036: The question about I2C Falling time of SDA and SCL!

Hi team,

My customer is measured I2C interface signal speed and they measured the falling time is around 1.5ns which is smaller than our specification-(15+0.1Cb) ns?

So could you advise is it ok or not?

If not, how to improve?

Another question is what is Cb value?

Or do they need to change pull-up resistor higher?

Thanks

Thanks