But then you need a surge in power to put it back from lo_temp to hi_temp when you get back home, I honestly don't know if it costs more or less than just maintaining it at hi_temp, and what are the orders of magnitude involved.

The first order approximation is that the heat loss between the inside and outside is linear with the temperature difference (delta-T) between them. So, if the delta-T is 10°C when occupied and allowed to rise to 14°C when unoccupied for 8 hours, there is a small savings. When the heating system is then commanded to recover the temperature, it will generally do a longer, single run (which for fossil fuel equipment is more efficient than a series of small runs, but for heat pumps is not significantly different [unless it engages emergency backup, which is far worse])

Overall, it's a small win, partially offset in the heating season by the heat gain from human occupancy and activity. It's almost surely not enough of a win to sum up to pay for the conditioning of an entire office building that would otherwise not be heated beyond "don't freeze the plumbing".

Presumably a 15 degree F or whatever lower temp (and reduced use of electricity for other purposes) during the day does reduce costs somewhat. However, for most people, commuting is almost certainly a significantly larger expense.