I have a large-breed pup myself (a Bernese Mountain Dog) and went through the same “how far can we walk?” question. The general rule of thumb my vet gave me was 5 minutes of structured walking per month of age, twice a day max, until they’re fully grown. So for a 14-week Spinone, you’re still in that shorter-walk stage, and the real “proper walks” will come gradually over the next several months.
What really helped with my Berner’s socialization and exercise without overdoing it was mixing in mental enrichment, short training sessions, puzzle toys, and little “adventure trips” to different environments. Like you mentioned, visiting towns or riverside walks is great because it tires them out mentally as much as physically.
If you want more ideas on low-impact ways to keep a young pup engaged and safe while they’re growing, I found some useful guides on Four Dog Paws to check out a few that focus on joint-friendly activities for large-breed puppies. It gave me a lot of peace of mind knowing I wasn’t pushing my dog’s joints too early while still giving him a full, happy puppyhood.