If say I had 15k metal, and consumed it (leaving 10 metal left), then a colony tries to scan my colony and check my resource on the same tick, will it output approx. 15k metal or approx. 10 metal?

If I had to guess I'd say the 10 since it is the computer actively computing it. It is not something like statistics that are only calculated during tick change but something must change as it occurs otherwise people could spend metal they didn't have. Just an educated guess on my part not entirely sure. I can test it on RC for you in the morning though.

Thanks. I was thinking of using those scans to check if a player's online by checking consumption (This especially works in Havoc to those using all the metal to create forces.)