Sorry, was under the assumption you had yet to receive it. I guess it's really up to you then. I tend to think that as long as I receive my card(s) within two weeks then there is no reason to deduct rating. 15 days is right on the edge but I would still go with a 5.0.
I always leave 5.0s unless there was a real big problem.. I only mark down shipping when I get cards in top loaders without sleeves or the card is coming out.. It's my pet peeve
Sorry if this has been pointed out already. Didn't read the other answers yet.
shipping is rated on a 1-5 scale, with 5 being defined as excellent. Although the lower scores are not defined with a term, you can assume the lower the number, the worse the experience, with 1 being the worst experience.
I would only leave a 5 if I felt I received excellent service. Anything less and you should be subtracting points. In a case where we all have real lives outside of trading cards, I would expect someone to warn you first before delaying or keep active communications if they have not sent.
4/5 is 80%, which is a B in most grading scales. Nothing really wrong with a B, but it's not an A. However, the scale here seems a bit tougher and dropping below 5 is a bad thing. All the more reason to make sure you send promptly!