@ann Tecno is awful do go there. For 15k you can't get a new Xperia smartphone so I would suggest the Lumia 535, Lumia 530, Wiko lenny, Wiko rainbow, HTC Desire 310, Huawei Ascend G6, Infinix race bolt, Infinix x505, Infinix surf.
As you can see, there quite a number, but if I were to choose under 15K, I will go with the Lumia 535 or Wiko Rainbow, great value for your cash. You can also add a few hundred shillings and go with the Huawei Ascend G6.