How long does it keep to have a visa after submission?

I apply luxembourg visa in Nigeria through Belgium embassy on the 9th July 2018 and today is 28 July but they said normal time for visa processing is 15days I don't know why is taking much time in my visa application my intend date of arrival is 24th July

Have you tried contacting them? Mind you it is holiday time so that might also put a delay on things as less staff working.

I don't know how to contact them I don't have their contacts

Contact details can be found HERE.