driver goes up to 1MHz (datasheet).
The PCA9685 is an I2C-bus controlled 16-channel LED controller optimized forRed/Green/Blue/Amber (RGBA) color backlighting applications. Each LED output has itsown 12-bit resolution (4096 steps) fixed frequency individual PWM controller that operatesat a programmable frequency from a typical of 24 Hz to 1526 Hz with a duty cycle that isadjustable from 0 % to 100 % to allow the LED to be set to a specific brightness value.All outputs are set to the same PWM frequency.Each LED output can be off or on (no PWM control), or set at its individual PWM controllervalue. The LED output driver is programmed to be either open-drain with a 25 mA currentsink capability at 5 V or totem pole with a 25 mA sink, 10 mA source capability at 5 V
The PCA9685 is in the new Fast-mode Plus (Fm+) family.
Shielded 22 AWG twisted pair cables have capacitance in the range of 100-240 pF/m. So the maximum bus length of an I2C link is about 1 meter at 100 Kbaud, or 10 meters at 10 Kbaud. Unshielded cable typically has much less capacitance, but should only be used within an otherwise shielded enclosure.
If it was me I would use two PCA9685 boards where the lights are, and have 32channels available there.
The source capability is only 10mA. I suppose that's more than enough for the led driver he linked.
Why not drive them from three separate PWM outputs.