You're asking about scaling down the major axis of a comet's orbit. To figure this out, we need to understand a few things:

* Major Axis: The longest diameter of an ellipse (a comet's orbit is an ellipse).

* Foci: Two points within the ellipse that define its shape. The sun is located at one focus.

* Eccentricity: A measure of how much an ellipse deviates from a perfect circle. It's defined as the distance between the two foci divided by the length of the major axis.

Here's how to solve the problem:

1. We need the eccentricity of the comet's orbit: The eccentricity varies greatly for different comets. You'll need to find the eccentricity of the specific comet you're interested in. Let's assume the eccentricity of our comet is e = 0.5 (a typical value).

2. Calculate the distance between the foci:

* Distance between foci = Eccentricity * Major Axis

* Distance between foci = 0.5 * 15 cm = 7.5 cm

Therefore, if the comet's major axis is scaled down to 15 cm, the foci would be 7.5 cm apart.

Important Note: The actual distance between the foci of a comet's orbit is much larger than 7.5 cm. This calculation is just a scaled-down representation.