The issue with very short production cycles is that it would force a lot more required activity on everyone, and therefore regular checking back.
Because we obviously have to balance the time bonus thresholds along the potential of an active & smart player, so with a 15-minute production cycle, it would be a requirement to use it very often, starting to stress certain people out.
However, the copper production will become a lot easier once you unlock the better buildings like the Shrine or Market.
It is a part of the challenge to optimize the economy so that you neither have too many copper coins, nor too less to keep the productions running. You have to find the perfect balance of all the available buildings.
In general of course we closely watch your feedback and how well you fare. Not saying that the overall output of copper coins has to stay as it is!