Make object fall faster

What is the size of the objects that want to fall fast? As flaviusxvii said your problem is going to be with scale and an understanding of how this scale is effecting the physics engine.

When flaviusxvii said your scale is causing an issue they didn't mean that if you increase the scale of the object they will fall faster. What they were talking about is the distance. So in unity the default is one unit is one meter. Your problem is going to be how far away you are viewing the objects.

For example. If you look up in the sky and see an air-plane flying across the sky is it moving fast or slow? You know that it is moving extremely fast but due to your perspective it appears to be moving very slow. This is because of how far away you are viewing the air-plane.

This effect is going to be what you are experiencing. You have very large objects so to make them fit on the screen you need to distance your view. This means that what you see as a small distance on screen, to the physics engine is going to be many meters.

How far in unity units is it to move your object from the top of your screen to the bottom? This value to the physics engine is in meters and to fall a number of meters takes alot longer than the distance you perceiving on screen (maybe a few centimetres).

So in order to fix your issue you can do two things (possible a mix of both) either reduce the size of your objects so they are smaller and don't have to travel as far, or increase the gravity force. Gravity in unity is a constant force applied to all movable objects to simulate gravity. You can increase the global force in ProjectSettings -> Physics -> Gravity Change this value until you have the effect you want.