Boundaries. Get some.

Tell them to stop or you'll trespass them.

Sounds almost exactly like Everybody Loves Raymond. Just tell them that you and you wife need space. Say it politely and respectfully but firmly and they will understand. Though, of course, I don't know them and no matter how you say "back off, we need our space," they may still get upset. I can only say good luck.

Watch a few episodes of the old TV show “Everyone Loves Raymond” - You are living one of the running gags on the show… Ideally you can get your in laws to respect your privacy. Personally I grew up two houses down from my grandparents and it was great. In my case the grandparents very rarely came to our house, but I was often at my grandparents house and both I and they liked that. But of course people are different…

They give up after only 15 minutes? Wimps! You need to get some decent stalkers who will stay as long as it takes.

The only response is to promptly move and make absolutely sure they don't know where you are going.

they do it because you allow it. set some boundaries, or better yet your partner needs to with their parents. and stick to them