I have a bunch of radios again, and chose to log my results again. I went with the consensus that 15 radio calls are better and checked that out. This obviously means a smaller sample size, but roughly the same amount of radios were spent (465 this weekend vs 500 last time):

         3* 4* 5*
Assault  3  6  1
Bruiser  2  2  1
Hunter   0  0  1
Scout    1  1  0
Shooter  4  5  2
Warrior  0  1  1

By Rarity:
32.3% Rare
48.4% Epic
19.4% Legendary

I currently have a level 14 Training Grounds, with a level 8 Radio Tent. Average max level was 18, with the occasional 19 or 17.

Looking at last event's data, we saw that over half of the 5-radio calls only gave Uncommon survivors. This weekend, we can clearly see that the 15-radio calls give a considerably larger amount of Epic and Legendary survivors.

Even with 35 less radios spent, that's 15 Epic and 6 Legendary versus 9 Epic and 1 Legendary. 15-radio calls are definitely the best use of your radios.