Does google maps personalize the walking time to your destination?

It does not take into account your walking speed but assumes a normal walking speed. From Google Maps help

What is the Google Map walking speed? Is this a constant value or does it change depending on slope?

Normal walking speed is about 3 miles per hour - It does not adjust for distance travelled, nor for whether you are on a road or footpath.
It does adjust slightly for slope - it decreases more for uphill than it increases for downhill.

A user wanted customized speed, like you do and they were suggested to raise a feature request.