No, because "fifteen minutes" is plural, and the "walk" doesn't come into it. However, you can say -- and I think most people would -- "a fifteen minute walk" (which you may also write as "a fifteen-minute walk"), in which it's the walk that takes the focus and "fifteen minute" is being used as a modifier.

Close, but wrong order. "It's only a fifteen minute walk." Also in "a fifteen minute walk" "minutes" is singular because "walk" is singular. vs. "I am walking for fifteen minutes"

' It's only a 15 minute walk away ' would work also :)

It's only a fifteen minute walk.