This is great! There are a lot of really great ideas here, and I like the overall mood of the piece. Maybe it's because it is in C minor, but I did feel a connection to the first movement of Mahler's Second Symphony.
Some parts I liked:
3:19 - I really liked the string melody here, and the half diminished chord at 3:45 is wonderful!
6:15 - Personally I liked the bold chords here that took me by surprise, although I will say maybe you should bring the piccolo down an octave, it seems a little overpowering.
8:30 - The brass here is lovely! I think it would be even better if you tried to add a countermelody in the horn or trombone, the whole notes are a little stale.
9:33 - I really like the clarinet solo, but similar to above I think you could spice this up with some countermelody in the other woodwind voices, instead of having them play just whole notes.
10:55 - The string pizzicato entrance here is really cool, and a welcome contrast.
Some thoughts I had for improvement:
4:40 - This flute note is held for a really long time. For one, it doesn't seem realistic for the player to hold the note that long, they will need to breathe. And two, it becomes a little stale after a while. Maybe have this note be exchanged between other instruments? For example - have a clarinet come in while the flute is holding, then the flute stops as the clarinet continues, but then an oboe comes in with the clarinet and exchanges similarly? I think the change in timbre of the instruments might keep this held not more interesting...
6:35 - I like the overall mood of this more bombastic section, but I think you could spice it up by adding some brass. They seem underutilized in this section. The timpani at this part I think could be enhanced by have the brass play chords on the same rhythm for example
I would split the horns into two staves, having all four on one gets a little jumbled.
I think the climax at the end kind of comes out of nowhere, I think it could use more buildup.
11:45 - Add slurs to the woodwind technique here, I don't suppose you expect them to articulate all of that fast technique?
I'll echo what others have said about the organization and structure. There are a lot of good ideas, but I don't think they are always connected well. If it were me, I would distill this down to and handful of ideas and try to develop those more, while also working on smoothing out the transitions between sections.
I mentioned this earlier, but also work on adding more counterpoint and countermelodies. There are several places where a melody is accompanied by whole notes, when a countermelody could add interest. The best way to experiment with this is find a place where the melody has a longer note and experiment with giving one of the other voices a countermelody behind it.
Overall really great work, thanks for sharing! I look forward to hearing the rest of the completed symphony!