Name appears twice in 15 days

[nishkrish]

i want to run a check if the same name appears twice in fifteen days of
period. should i write a macro or a function if so which function

 

[nishkrish]

i have same data column A is Date column B is Name but its a running database
i cannot sort or dont have time to take it to different worksheet and work
like this i want either to write a macro which will automatically check for
name once you type in or write a function.