Lower the barrier for entry to the Leading Organizations to 15 MRs in 3 months

Why is this change being made?

As discussed with @esalvadorp we are reducing the entry requirements to the Leading Organizations program to 15. 20 was too steep for many organizations to reach, and after analyzing the numbers, 15 was a more approachable number, allowing us to include organizations that are really trying and are committed to the program.

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