Can I get breast implants at 15 for uneven breasts with parental consent? Or do I have to wait until I'm 18?

Whether you can have implants depends on your surgeon's philosophy and if your breasts have fully developed.  I personally would not extend that service to you at age 15. 

Breast augmentation in a teenagers a touchy issue. Nevertheless, the occasional teenager may be a good candidate for the operation with parental approval.

Thank you for your question.  Without photos I have to guess from your question that you have at least a cup size difference between your breasts.  If that is the case then you may want to consider reducing your larger breast to make it closer in size to the smaller one.  In my opinion that would be the best way to go for a couple of reasons.  First of all, you will get better symmetry which will allow you to wear those swimsuits and cute clothes now until you are old enough  for breast implants to be a reasonable option.  More importantly, by reducing the larger breast, when it is time for breast implants your surgeon will hopefully be able to use the same size on both sides.  While it is certainly possible to make uneven breasts the same size with different sized implants, your breasts may still look very different  and over time may become even more asymmetrical.  The larger the size difference, the more this is true.  The reason for this is that the smaller breast gets the bigger implant which will probably be a very tight fit.  This will result in a breast that will be high and "perky" and will tend to stay that way or perhaps drop just a little bit.  The larger breast gets the smaller implant which will be a loose fit and may not even give the breast any lift at all.  While you may be able to look symmetrical in clothes, out of clothes you will have two very different looking breasts.  In fact, even if they are exactly the same volume, the smaller breast with the big implant will probably appear larger than the other one.  The other thing that will happen is that the larger breast will fluctuate more with weight gain and loss meaning that you will always be dealing with changing differences between your breasts. To fully explore your options You should have a consultation with a plastic surgeon certified by The American Board of Plastic Surgery and preferably also a member of The American Society for Aesthetic Plastic Surgery.  Finally, he/she should be able to show you before and after photos of their own work on patients that are similar to you.  I hope that helps.