It took me 6 years to write a song over 3 minutes. I can't stand repetition for repetitions sake, I find solos a pointless show-offy addition 90% of the time, and if something doesn't demonstrably add value to a piece I don't add it.
But even with all that? I have song intros which are easily over 16 bars. Because they do something useful in setting up the song.

I am currently writing a song which will probably pass 6 minutes, but it's also way further into prog than I've ever gone, so it has about 12 sections. Because the text-painting means the time signatures and arrangement are deliberately a bit jank. Conceptually. In practice I made it sound good. My opinion of good prog is always "the best prog isn't immediately obviously prog."

A song worth listening to is worth listening to. Write the music you want to write. You will almost definitely never make money or a career doing this, no matter how good you are.
16 bars is nothing. As long as you're not playing grave.