You guys sure romanticize the early period.
I enjoyed the first two weeks because it was new and honestly my wife could use the help.
After that, babies weren't really my thing because it was a constant struggle to figure out what they needed.
I prefer the 1-3y old period, they start walking so you can do more stuff with them + when they start pointing/talking it is so much easier to take care of them.
During this period I took quite a bit time off to spend more time with them, especially with the oldest (youngest is more of a momma's girl).
Now after 3 I just make sure to be home on time during the week and occasionally take them to do stuff.
With regards to your question: take the 15 months but don't spend it 100% with the kid, make sure you still have time for yourself & friends so you don't end up frustrated.