Help Particle distance problem

[IlyaZzz]

Hello.

For my project, I need to simulate coins in a bag.
And when I throw coins there, the following happens:




This is inside:



The mass of the coin is equal to the mass of the particle in the bag (0.01)

These are my solver and cloth settings:



So, how to get rid of stretching the package?
How to make a fixed distance between particles?

Upd

And I have one more question.

How to optimize coin collision? 
When I have 50 of them on scene, I have big problems with my performance...

This is the coin settings:

So, does anybody know how to fix it?