Is it still not enough long for a Fantasie?
If you want my opinion, it's a little on the short side. ~4 minutes is better than 3, but you take a piece like "rhapsody in blue" by Gershwin. A typical performance is 16 to 20 minutes long, depending on the interpretation of the tempo. Why look at rhapsody in blue? It's written in rhapsody form. And it's a beautiful
piece, isn't it? At any rate, a Rhapsody is like a fantasie (also spelled fantasy), compositionally speaking. Both are for the most part free-form works. But why do people like rhapsody in blue? It's because there is some method to Gershwin's madness! There is development and with the score space allotted, he did a nice job of organizing his musical episodes and having them fit together cohesively
. I wish I could say the same about your piece, but I feel there needs to be more development. To master writing for large scale, I think one must master smaller scale. Have you written for piano? Getting good at music composition means putting in your 10,000 hours. Just like piano, or whatnot. That's my thinking, anyway, FWIW.