I bought shares in our company at 15% less than market value I think it was 2 years ago. My questtion is when was this BIK tax introduced on company shares and do I need to inform tax office and if so will I incur a penalty for not informing them before this ?
Yes - You should declare the 15% as income in the year in which you bought the shares. You may well find that your employer has informed Revenue, or will do at some point in time.
and if so will I incur a penalty for not informing them before this ?
If you proactively 'fess up to the issue now, it is unlikely that you'll be hit with a penalty. You may be hit with interest on the outstanding tax amount - AFAIK, Revenue have little discretion over applying the interest.