Is an annual return of 15% usual? And can you explain why or why not

It depends how high the risk is.

If you’re referring to return on investment of savings, that would be a good year in my experience. Better than usual.

It is high as the s and p 500 including dividends has returned about 11.7% over the last few decades but closer to 7% historically over its entire history.

In Canada annual return refers to a statement that the business is still operating.

15 is high as a long term average.
For a short term it could be higher.

An annual return of what?