How to fly a drone in Class D in Italy?
The class D airspace you are referring to is a control zone (CTR). According to article 24 of Regulation for Remotely Piloted Aerial Vehicles, the following applies to VLOS operations (emphasis mine):


Except as required by point 6 below, RPAS operations shall not be conducted:

a) within ATZ and beneath take-off and landing paths or at a distance less than 5 km from the airport (ARP or published geographical coordinates) where ATZ is not established;
b) within CTR, without prejudice to point 5 below;
c) within active restricted areas and prohibited areas.

Operations within CTR are permitted only to RPA with operating take-off mass less than 25 kg, up to maximum height of 70 m AGL and within maximum horizontal distance of 200 m. Beneath take  off  and  landing paths, beyond ATZ boundaries and up to 15 km from  the airport, maximum height shall be 30 m AGL.

When  operations  do  not  meet  the  requirements set  forth  in  points  4a), 4b) and  5 above, operations shall be  carried  out  according  to  procedures  published  by  ENAC. When it  is required to operate within airspace as referred in point  4c) above,  operations  shall  be subject to specific authorization according to procedures published by ENAC.



Although you are pretty much directly below the approach path to Linate's runway 18, since the park is just over 15 km from the airport, you should be OK to fly up to 70 metres above ground as long as the drone stays within 200 metres of you.
Of course, there are also other applicable rules to consider: for example, you must wear a high vis vest with &quot;Pilota di RPA&quot; printed on it, you are not allowed to overfly crowds (including wedding guests) and the drone must be registered and identifiable.