I got bitten by stray dog.but in clinic they do not have rabies vaccine as there was no case of rabies recorded in last15 yers. should i still worry?

Regional issue: Across the US local health departments are part of a network that keeps up with regional rabies activity. This includes any animal found with the disease in the region. If/when there is no rabies activity in the region, the general advice is not to undergo the pain/expense of the shots. You can call your local health department to confirm this is what is proper for your area.