L.P.
Hi N.,
I moved to California from Oregon when I was 19 and 2 of my 3 kids were born here. I drove home every year for either a holiday or a summer visit since my son was 6 weeks old and my daughter was 2 years old. That is 10-12 hours in the car.
My best trips were leaving at 4:00 in the morning and they would sleep for several more hours and by then I was ready for a stop. I would let the 2 year old run and play for an entire hour and feed and change the baby. The future stops for the baby were shorter. That evening I kept the kids on schedule and they slept great.
Traveling at night is difficult for the parents. I tried it ans tended to get very sleepy on the road even with coffee and a nap previous to the trip.
For the 15 month old. Don't forget a busy bag of things to do and snack bags. A music player with head phones is good too with fun kids music. Don't hesitate to pop one in the CD player once in awhile either and sing with her. If you treat it as fun she will too.
Good Luck,
LLP