There are several routes to see the Last Supper, but my recommendation is the route from Cadorna Station on the subway.

The road from Cadorna Station to Santa Maria delle Grazie is the same road that Leonardo would have walked from Sforza Castle to Santa Maria delle Grazie about 500 years ago to paint the Last Supper.

If you actually walk the same route, you will find that Sforza Castle is surprisingly close to Santa Maria delle Grazie and it doesn't take much time.
Leonardo would have taken the shortest route across the courtyard to the dining room where the Last Supper was painted, but we made a big detour and visited from the side of the church entrance.

Nowadays, it is completely reservation-only, so it is not easy to visit, but if you enter the remains of the dining room where the Last Supper was painted, you will be overwhelmed by the unexpectedly large walls.
The ceiling is high inside, and the voices echo well in the deep space, enhancing the solemn mood.

Much of the interior of the building was destroyed during World War II, and the white walls, with half of the decorations still missing, are somewhat bleak. Apart from Leonardo's Last Supper, there's nothing to see except the Crucifixion on the other side, so you get bored of it surprisingly quickly.

When I visited 30 years ago, there were no time or number limits, but almost everyone who visited left within 10 minutes.

The current 15-minute time limit may actually be a surprisingly good time allocation.

 

 

 

 

 

 

 

The Last Supper Tour Guide: There is a very detailed explanation on the Japanese website.
https://amazing-trip.xyz/t-blog/vinciano-reserve/vinciano-seeing/