This webpage shows what's special about March 15: https://www.checkiday.com/3/15/2019
For example:
Dumbstruck Day is being observed today! It has always been observed annually on March 15th. When someone is dumbstruck, they are so shocked and surprised that they can't speak. People may be dumbstruck after hearing amazingly good or amazingly bad news.
Dumbstruck Day = D Day!