Is there anything I can do to get nipple sensation back?

Thank you for your question.  After this amount of time, it is not likely that the sensation will return.  I'm sorry you feel it was a mistake, unfortunately this does happen to small percentage of women and can be a side effect from breast augmentation. If you would like additional information regarding breast augmentation, you can download a free copy of my Breast Augmentation Planner at ABetterBreast.com.Best of luck to you. 

Nipple sensation can change (hyper\hypo sensitivity). It is very uncommon for nipple sensitivity to not return at all. After 15 years it is very unlikely it would return. A possible solution would be to decrease your implant size but there is no guarantee. Speak with a board cerified plastic surgeon.  

After 15 years it is very unlikely that it will ever return. I do not think that a nerve that has been stretched for that long or maybe even cut will come back. You can seek some advice from several surgeons but I do not think you will ever get the sensation back.