You should certainly try for DI if you can, as your current team could probably do okay (with some upgrading). Remember that you will get higher attendance and more TV money to upgrade your rosters and pick up some 18 year-old trainees. As such, you will likely be able to make more as a 5th or 6th place team in D1 than as a 1st place team in DII.
Of course, you should be picking up solid trainees as you can afford it, and they will quickly surpass your other players in skills.