TacticalFailure

Recently promoted to League Two from VNL and VNN. Been a bit since I've played a low league, and still somewhat new to FM, but squad registration is requested for L2. It states I need a minimum team size of 15, but the issue is I have only 6 players that are not U21 or GKs out of 28 players. Even though U21 and GKs don't need to be registered, do I need to still register some of them just to meet the 15 minimum? So just pick the important players and register then anyway?