put baby down awake
The mistake people make with this is they assume you jump straight in putting a baby down fully awake and hoping for the best.
In the time it takes to accept this isn't going to work, all manner of poor quality sleep habits develop. So perversely, the problems come from trying to do the right thing.
Putting down asleep is not difficult and they can all do it. But it's gradual. You don't jump in with both feet.
So at newborn, for example, a feed will make baby sleep. Its what it does. Y0u then wind and as part of winding I would not aim to keep baby sleeping, the winding might be just robust enough so baby isn't in the fully deep sleep. Still asleep, but not floppy asleep. Then put down.
15 weeks I'd be feeding to dozy. Then winding and putting into swaddle gets baby used to being moved around when sleepy. Dummy in upon being put down and swaddle to calm startle reflex.
At this age is really is not about putting down a wide awake and distressed child. It's about cuddling baby until calm, quiet, just asleep and baby being used to being moved around and being resettled during that 'going to sleep' phase.
Compare to a baby who is used to not being disturbed or moved until fully and deeply asleep. Where mum and dad are afriad to move an inch so's not to disturb the baby whos finslly gone to sleep. That's the baby who will struggle to be 'put down' to sleep. Even though both are cuddled to sleep.