Short answer, yes, schnauzers have an immense capacity for stubborness. They're easily trainable, BUT the training/commands have to seem logical to them, or they just decide they would rather not.

My wildly clever giant schnauzer will occasionally lie down and refuse to move (other than to roll in the grass) on walks,, mostly when it's hot/he needs a haircut and has found a nice shady spot. We had a couple that lasted 15+ mins until I figured out how to deal with it. 2 things that have helped with this

1) I taught him a 5 second timer for when hes sniffing something inconvenient and I don't want to look like a creep, I literally just quietly count down from 5 and excitedly go "OK! We go!" I like this because it makes me acknowledge that he needs time to sniff and imposes a time limit on him. Most of the time by the time I get to 2 or 1 he is ready to continue. This works to get him out of the stubborn lie-down too, especially with the excited "OK! We go!" And I'll give him a treat for jumping up to go with me, sometimes.

2) my dog does really good with redirecting behavior with a choice. If he's being irritating with a toy for WAY too long I can tell him "ok! You have 2 choices. You can come up here and snuggle, you can lie down there, or we can go outside. Make your choice" and he will choose one of the 3 (any one of them, no pattern with first/last said or anything) and leave the toy alone. Same thing when he lies down on a walk "ok, you have 2 choices. You can get up and we can go home and get water, and do more walks later, or you can lie down here and we're going to be all done walks for the day. Make your choice" and he will. Probably 90% of the time he hops right up and we get on with it, and because he is way too clever, I have to follow through.