I think you will notice little or no change with a 15-day course.

He had noticed a change in the air of the city.

Teachers noticed a change the first day he took over.

Whether you are going to notice a 1% change in a 50-100 year period is another matter.

He was rather more than a year old when I noticed the change.

When the reading was over, I noticed a complete change in the mother.

But, even as last year, she noticed a change in me.

It has been about 5 months now and I notice a change.

In the office, you don't notice the change of season.

Something pulled me away, although I didn't notice the change very quickly.