Greece to Italy by ferry

Can you give us assurance that you are capable of personally flying like Superman does? Without that capability, you cannot do it. Take a map, put some pins in it and understand the distances involved. Reduce it to maybe seven locations, five or six would be better, and then come back for some practical suggestions.

Is this a joke????

15 days is just way too little for what you want to do.

If you start out and do a rushed tour, it would be something like:

Day 1: Arrive Athens
Day 2: Athens
Day 3: Travel to Meteora
Day 4: Meteora
Day 5: Travel back to Athens, Flight to Santorini
Day 6: Santorini
Day 7: Travel to Mykonos
Day 8: Mykonos

And you are already over half way through your trip. Rushing through the rest, you are looking at maybe ~25 days total.

Some points to consider:
Except for the Capri/Sorrento/Naples/Amalfi coast area, figure that any travel between places takes up a full day...yes, you will have some time at the place you are leaving and some time at your destination that day, but figure each stop is two nights minimum, one day of travel, then one day uninterupted for seeing what you traveled to see.

For the Naples area, for what you want to see, figure at least three full days there.

The above itinerary would also rely on flying to Santorini, flying back and forth to Zykanthos, flying to Naples. I would skip the ferry to Italy from Greece, that takes 2 days of travel.

I suggest a second shot at a list. What are the most important things to do? Concentrate on Greece or Italy, not both? Can you devote more time and expense? Is cost a big issue or small, if big, then less travel will save you money, Greece maybe cheaper than Italy. When were you planning on going? That can make a big difference in cost. Many, many more questions, but first is trying to come up with a reasonable itinerary.