China’s biggest banks lowered their benchmark deposit rates across the board for the first time since 2015, a move designed to help them boost lending to shore up growth in the world’s second-largest economy. Seven major banks, including Bank of China Ltd., Industrial & Commercial Bank of China Ltd., Bank of Communications Co., and the Agricultural Bank of China Ltd. on Thursday cut deposit rates on a range of products, including demand deposits, three-month and five-year deposits. At some lenders, rates for one-year deposits were cut by 10 basis points to 1.65%, according to the lenders’ websites.