First off, 16va is definitely incorrect as explained in the answer to this question and I'm surprised your software lets you write it. The correct ottava notation is 8va/8vb for one octave up/down and 15ma/15mb for two octaves up/down.
As for how often you should use them, I would say sparingly, but it's largely a matter of taste, and will depend on your audience. You may think ledger lines are difficult to read, but frequent changes of octave can be difficult to read too, as can changes of clef. Less experienced players who aren't very confident reading music may well find the ottava notation helpful, but more experienced musicians who are used to ledger lines are likely to find it annoying if overused.
One thing ottava notation is good for is for making it very clear if you're repeating a phrase up/down an octave or two. Also, if you're writing a piece for beginners then it can be a great way to get them exploring the keyboard before they've learnt about ledger lines.
Unless you're going very, very high or very, very low or really, really want to avoid ledger lines then you'll rarely need 15ma/mb. You can cover all the keys on a piano with 8va/8vb and a couple of ledger lines.