It is a long time since I was last on this site, and I have missed hearing your compositions. It was a delight, therefore to find this fragment. I have listened to it half a dozen times, each time hearing it more clearly. I have also looked over the score, although I do not have perfect pitch so I am unable to 'hear' music this way.
First, the piece is exactly as you entitle it: a call to adventure. Having watched a great many action and adventure movies, your piece fits the genre perfectly. Well done. I was not reminded of The Shire, despite having watched The Hobbit and The Lord of the Rings trilogies many times. If pushed I would say that there was the very mildest of resemblances to the Pirates of the Caribbean theme, but less Irish and more English, somehow. I am more reminded of the Westerns I used to watch many years ago as a child. So, I do not believe you have any reason to be anxious that your composition is specifically derivative.
Second, on first listen, there were several places where the simple rhythm got a bit lost. On listening more I could hear that, in fact, something more complex was going on, as I would expect of serious music. However, in my stereotyping of the genre, I would say that the simple rhythm needs to be obvious, although not necessarily forefronted, throughout any 'A' sections. In contrast to what I have just written, were I listening to Sibelius, I would expect to hear simple rhythms become increasingly complex, which is ultimately more interesting.
Third, on listens after my first, I was very keen for the piece to continue. Specifically, I was looking towards a somewhat darker 'B' section (perhaps then followed by a return to the 'A' theme).
Fourth, try as could, I was unable to hear the harp. From the score I knew the harp was playing, and I was looking forward to the glissandi, but I just could not hear them.
Fifth, and following on from four, I am going to be very bold, inasmuch I am sure that many others on this site are able to advise you better that I ever could. I think that if you want phrases on specific instruments to be heard, then you need to make holes in which that can happen. In my limited experience, this seems to apply especially to the quieter instruments. I did hear the xylophone, albeit only once, towards the end of the piece. Of course, the other obvious way to handle this would be to include several harps, etc., so as to increase their sound volume in relation to the other, louder instruments.
Sixth, I liked the balance you brought between passages in which multiple threads were being pursued, passages that were harmonious with the theme/melody, and passages that were unison, emphasising the theme/melody. That balance, it seems to me, fits well with the genre.
Orchestral music is usually my preferred musical environment. I am, therefore, excited that you are interested in adapting your talents to include orchestral music. I look forward to hearing where you might take this piece, should you develop it further, and to future orchestral pieces you might compose.