Puppy starts whining on structured walks/outings. Just boredom? Suggestions on how to work through it?

I've got a 14 week old pup and I'll take her to dog friendly stores or walks around the neighborhood or greenway. I'm trying to work on her heeling and paying attention to me. She's pretty good about not pulling, thankfully. But she'll start giving me the occasional whimper and I'll have to coax her to keep going.

It's NOT a distance issue. If I give her the free command where she can go sniff around and do her own thing, she's fine. I'll go on walks with my friend and his adult dog and she'll go off leash there (his dog keeps her within bounds as her recall isn't 100% yet). We have walked about 3 miles while the dogs have been doing circles around us and she still had energy to keep playing.

I'm guessing I just need to lower my expectations of what I can get out of my puppy focus wise at this point. Any suggestions of how to balance tiring her out (on top of playing) and building the distance on structured walks? I don't wanna give in to letting her run around like crazy (even leashed) all the time, as I want structured heeling to be the default expectation.