The depreciation of Indian rupee against the US dollar is expected to push the country's import bill by about $15 billion, think tank GTRI said on Thursday.Compared to December last year, the Indian Rupee (INR) has depreciated 2.34 per cent against the US dollar, moving from Rs 83.25 to Rs 85.20, while the Chinese Yuan has weakened by 0.06 per cent, the Global Trade Research Initiative (GTRI) said.