Do you value your time at $0?

The parent wrote "on top of that, [..] 2 hours of extra free time". So they didn't include time valuation to the 15%.

Here’s an example of train commuter fares in the Bay Area: https://www.caltrain.com/fares. Travel from San Mateo to San Francisco (3 zones, around 20 miles) is $200/month. That’s the discounted fare for a ticket. It doesn’t cover parking or travel to/from the train. If you need transportation to/from the train it can add another $50-$100 per month for fares, or more for parking fees and gas consumption for drivers.

And BART (a different rail system) is even more expensive.

That’s not negligible: that’s almost three hours of work for me to cover the cost (pre-tax). And I’m fairly well paid. Most engineers aren’t paid half as well. It’s a much bigger hit for them.

I assume that's just a bus/subway pass? At least where I live, parking at the train station, a monthly train pass, plus a monthly transit pass would be something like $500 or $600 dollars. To say nothing of taking almost 90 minutes door to door.

Yes that's the scale for monthly public transport ticket price in large number of continental European cities. I don't own a car so I may be out of touch with those expenses, 15% just sounded to me like a lot.

The time value is of course then on top, but the parent accounted for that separately.

A monthly bus/subway pass in the local large city is in that range as well--about $90. But, as in the Bay Area example, that starts going up quite a bit if you take rail that goes beyond the bus/subway system.

In Boston, if you don't have a car you almost certainly wouldn't be taking commuter rail with fairly few exceptions.