There is an old Chinese proverb 'The best time to plant a tree is 20 years ago. The second best time is today'.
It is never too late to start, and even R15000 is good for a start. As you pointed out you will be adding surplus cash to the amount. If you stick to that then you will be surprised by the amount you can accumulate.
Like others have said, get rid of your debt first. You pay more interest on debt than you will ever be able to get on a investment.
You options regarding investments is many.
EDIT: Nevermind, just saw you mentioned risk-free.