I'll join in to give you an example of where you don't want to be when your babies ate 15 months old......
Ds has never napped well but through the summer we fell into a reliable two prams naps a day routine. It did mean me walking home, and often he would wake up soon after I stopped, but he went off OK (having spent months napping on me or in the sling)
But winter is coming, he's started being difficult to get to sleep on some occasions, and I'm 6 months pregnant. Somethings got to give!
I work three days a week but on my two days off last week I put him in his cot for a nap. Sat with him, curtains drawn, mobile on. Both days he took 20-30 minutes to nod off, bit of tired moaning but not real crying. First day, slept for 2hrs 20 before I woke him. Just the one nap. Second day he'd had 30 minutes in the morning in the pram, but still slept for 1hr 40 ish before I woke him. I was thrilled!! Saturday came, he spent 2hrs15 in his cot over two sessions, not bloody sleeping. No nap all day. Same again Sunday though I only tried once.
So today is a day off, he napped in the car this a.m. And I'm about to give up on a pm cot nap as it's getting two late. He's tired, but won't give in. Ffs.
I think I need to do the same as a pp and take some time off.
I think for me at this stage, the timing is crucial, I think we've gone past it this afternoon.