You're getting better!
I wish I knew how to solve your file size issue, but I will say that sound is the biggest issue in this one. Aside from volume levels being off for the dialogue (some characters, like Julian, were quieter than others), it was unusual to hear efforts and reaction noises but no sound effects, especially when characters got hit in the face or were reacting to their environment. Too much walla/additional voices detracted from what was going on (I heard more people than I saw).
I'm not sure if mixing all the audio into one file first would help the file size problem, since it depends on how easy it is to animate to for the animator, but if you can convey the environment in a radioplay, it can very easily be translated into visual. More important sounds, like dialogue and meaningful SFX, ought to be a bit louder and easier to discern from the background sounds. You know how people can forgive bad visual quality on YouTube but will cringe and ignore video with bad sound quality? It's like that. Right now, the visuals are alright, but the sound is what's detracting from your work. If you're using Audacity, I'll warn you now that mixing with it isn't hard and not too bad if you know how, but it SUCKS at adjusting volume levels (which leads to me using Wavepad in combination with Audacity sometimes).
As a whole, look into what's causing that file size problem. Things got really interesting just as it ended and though it makes me want to see more, I'm still getting an incomplete vibe (when I know better). If you need some help with some mixing and SFX, I can help ya out too~