I'd just stop hand pollinating. The plant will likely self abort any fruit that it can't handle. If you see that the weight of the fruit is too much I'd try and rig up a support. If that doesn't work then removing fruit might be necessary.

I totally agree with Karyn. If nutritionally the plant cannot handle all the fruit, it should thin itself out without you having to intervene. Fruit trees like plums do this all the time. As for physical limitations, I would build something to help with the weight. Also, I have seen P. edulis plants with way more than 15 fruit. Enjoy, and be happy you can grow them so successfully!