Is it possible to use 400 kHz I2C buses with a 32 kHz slave?
read the data sheet to determine if the slave's MSSP can support the speed your interested in.

If you need extra time to copy the data out of the receiving register use clock stretching, again read the data sheet for the slave for proper usage.

EDIT: from the datasheet for that part, 400khz requires minimum device speed of 10Mhz, 100khz requires 1.5Mhz.