"So the DC monsters need to beat is 16 or 17. At first level."
Huh?
Point buy and str array gives you a 17 cap on abilities at 1st level. For +3.
Proficiency is +2.
That is passive percrption of 15 assuming that's the lead guy at first level.
So, a wolf being sneaky needs to roll 15 - not 16-17 - since contests like this have ties go to the prior status- the wolf was unseen before the check, so tie does not reveal the wolf.
With stealth +4 that's z toll of 11 needed do 50/50.
Flip the situation, PCs sneak up on wolf. Wolf gets advantage due to keen senses and so has passive per of 18.
That's gonna require that first level sneaker with +5 net bonus yo roll 13+. So, a little tougher.
Now, the outlier might be s variant human taking like observant at first or one of the dex+1 to get to 18 dex. But nowxwexare into very specific outliers, not routine play.
By tier-2 and lateer tier-1 with magic, this changes of course.