There was a
THREAD about this very same subject a little over 2 months ago stating a 14 character limit. As I stated in that thread, I can save contacts with over 50 characters in the default Note 4 contacts app. The thread was unresolved because the poster never returned. This is a contact I just created. It has 44 characters, including spaces. Note that my phone is still on Kitkat, but I would think it shouldn't matter.
If you can give us more specifics about what you've tried, or what you're doing, it might help. Are you using the default contacts app? Have you tried clearing cache on the contacts app?
In reality, I have no idea what might be causing it, but find it interesting that this is the second post I've seen on the subject. Might be OS, or even region related.
Gee... I could have sworn I hit the "b"! LOL!