Ping 1.1.1.1 -n 15 -w 1000 > nul
1.1.1.1 is not a public address. It is non existant. You can substitute your local host if desired.
-n 15 is the number of pings to be sent
-w 1000 is the time, in ms, to wait between pings (1000ms = 1 sec)
As I stated before, it is not perfect, but is close enough.
the first ping gets executed immediately
Its almost immediate. So adding an extra second will make it more accurate. However, there is a small amount of overhead so it would be slightly more than (time). Slightly over or slightly under, in this case, probably does not matter.