@Emiliano124 If you have your booking settings correctly set to 15 days maximum stay, you aren't doing anything wrong.
Inquiries are simply a way for guests to ask questions and a guest can ask to bring their pet rhinocerous if they want, there's nothing a host can do about that.
It's annoying, for sure when guests ask for things which are clearly not offered in your listing, so all you can do is message back saying something like "Thank you for your inquiry- my listing has a 15 day maximum stay, as is evident in the listing description. You need to look for listings which accept longer term reservations."
If you get a lot of these inquiries, create a saved message you can just send each time so you don't need to write it out.
You could also state prominently in your listing description "Please note: this listing has a 15 day maximum stay length. We don't accept longer bookings"
And FYI an Inquiry message doesn't require that you click on pre-approve or decline- just answering the message within 24 hours is sufficient.
@Pat271 Just because a host has a 15 day or whatever length max doesn't mean they can't host longer bookings, it can just mean they don't want to. I've always had a 2 week maximum because I figured if a guest was objectionable in some way, I wouldn't want to get stuck with them longer than that. And as a homeshare host, I don't want a full time roommate.