14 hours is definitely enough to leave the airport during a layover. The exact situation depends whether you have 1 booking or 2 separate bookings. You need to make sure to check-in for both flights. Checking in for the first flight does not mean you are checked in for the second. In both cases, you can then exit the airport but make sure to leave adequate time for pre-flight checks when you return. If you have 2 separate bookings, you will need to collect any checked-in luggage and re-check it when you return.

You do not need a visa, Italian citizens can enter visa-free for up to 90 days.

  [1]: https://www.mfa.gov.tr/general-information-about-turkish-visas.en.mfa