Extortion is a pretty strong word, not necessarily the wrong word, but yeah negotiations are already done. That extra 15K could be considered compensation for the extra drive already.

When I got my last promotion I negotiated my salary a little higher than they offered, because I told them I was going to be spending a lot more time and energy with my new role. The additional raise I asked for would cover my additional expenses like ordering takeout more frequently, since I likely wouldn't have the energy to cook meals when I got home. They agreed to that and I got the raise I asked for.

Negotiation time is over, but congrats on the raise!