delete other similar entries with timestamp <= timestamp+15min?

Hello,

I don't know how to do the "pseudo-delete" in the middle:

select * from table order by stamp;

nr | stamp
----+------
1 | 20:45
1 | 20:46
2 | 21:00
1 | 21:03
3 | 22:05
2 | 22:05
1 | 22:06
1 | 22:06

"delete from table where nr is not unique during stamp + '15 minutes';"

which should end in a table like

nr | stamp
----+------
1 | 20:45
2 | 21:00
1 | 21:03
3 | 22:05
2 | 22:05
1 | 22:06

Is that possible in SQL?

Thanks,
Knut Sübert