What level is your campaign?
The Game has no level. I have never followed the idea that a campaign must have a set difficulty rating. While I recognize why this restriction is placed on modular adventures (set for certain levels) and is used for video games (difficulty levels), it does not seem realistic to me. Therefore, I have sought to avoid such restrictions.
From what I can tell (and I am no expert on any edition of D&D rules), in official D&D, a low-level character simply could not survive travelling with higher level characters or facing more powerful creatures. The rules (saving throws, automatic damage, certain powers/abilities) simply don’t allow it. By not following that system, I have not fallen prey to that trap. A 1st level character could roll super high and save vs a powerful creatures effects, and he/she could shoot that arrow that finds that chink in the armour of that great beast. It does happen and it should. What level is Bilbo’s adventure to Lonely Mountain in The Hobbit? What about the adventure to destroy the One Ring? The Fellowship surely consists of a variety of ranging levels yet they all go together. This is how it should be.
Therefore, our campaign has level 1 characters adventuring with level 30 characters (level 15 in standard D&D). It poses no problems. I don’t set out consciously to select encounters that are based around a certain level. Instead, I always seek realism and to produce encounters that make sense based around locale, etc. Granted, this means that at times the Party deals with an encounter easily or faces an encounter that is extremely difficult. Such is life.