According to The Way Forward agreement a time change of the magnitude envisaged for a lot of offices would constitute major change and would mean a full repick. Whether it does or not is a different matter.
You then ringfence duties for family friendly (as you would do for people covered under the Equality Act)
If your office is only moving 15 minutes it is unlikely there would be any real issues for people to all of a sudden need major changes to their duty structure to allow for family friendly duties.