I certainly don't think you'd lose the biofilter in 15 minutes. I'd guess you'd be pretty safe for up to a day, at least. I once left a bio-only canister, relatively clean, off for a weekend (accidentally), and it seemed to work fine when I turned it on Monday morning. I had some ammonia when I discovered the error, but it cleared soon after turning the filter back on. I wouldn't do that a regular basis, of course...
Did you say the filter had been running one week, meaning that a week ago it was not on a tank? If that's correct, I'd think there weren't many bacteria in there to start with.
Jim