Question: Do you have advance purchased discount tickets on a Freccia train from Milano Centrale to Venezia S. Lucia?
If so, at what time is the departure from Centrale? With a Swiss Travel Pass you can take alternate routes that avoid those quick changes, leaving a little earlier.
Also, I note from the actual train schedules, that the train you are changing to, an RE 80 coming from Locarno, will already have arrived at Lugano and will be waiting on Track 1 for your train to arrive. The hint is that it spends a total of 9 minutes sitting in Lugano. Normally trains only spend 1 or 2 minutes in a station, time enough for people to get off and on. It appears to be sitting in the station waiting for your train from Luzern to arrive and allow connecting passengers to make it on.
I swear the Swiss have had people with stopwatches (Swiss ones of course) checking to make sure that people moving expeditiously to the new platform can make it comfortably.