YOU SAID:

i am going to work in 15 minutes

INTO JAPANESE

私は15分で働くつもりです

BACK INTO ENGLISH

I'm going to work in 15 minutes.

INTO JAPANESE

私は15分で仕事に行くつもりです。

BACK INTO ENGLISH

I will go to work in 15 minutes.

INTO JAPANESE

私は15分後に仕事に行きます。

BACK INTO ENGLISH

I will go to work in 15 minutes.