Based on these comments you made:
- What I try to say is something about approximately 15 minutes ago
- doesn't using '15 minutes' make it to sound more accurate than using 'a quarter'?
- a word less is really better
It sounds like you are looking for a concise way to say an approximate time.
My answer is aimed at suggesting a short phrase that means a short but unspecified amount of time. (I'm not looking to give you a phrase that is exactly equivalent to 15 minutes, or 15 seconds, because I don't believe that's what you're after.)
With that in mind, I suggest the phrase just now:
The elevator is not working, but it was working just now.
Collins defines just now as: "a very short time ago." Vocabulary.com defines it as an adverbial phrase meaning: "only a moment ago." TFD defines it like this:
just now a short time ago : I came from a meeting just now where the governor said he would veto the proposed law.
The phrase could be used to mean a few seconds ago, or a few minutes ago, depending on the situation.