Ques. Please suggest dual Sim smart phone in the range 10-15k
Ans. At the lower price bracket you can look at the Lumia 640 or get a 640XL for an awesome camera, but do note it's a phablet.
If you can go a bit higher we would definitely recommend the Asus zenfone 2 ze551ml which is an awesome deal for the specifications it offers and has 4gb of RAM which was previously never heard of in mobile phones. This phone will not get obsolete even after 3yrs of its launch, unlike others which after 1 year of launch are unable to compete in the specs department even with budget phones.
It even has fast charging wherein a 10 minute charge can yield you a 4 hour 2G talk time.