Health insurance rates for more than 1.5 million Californians covered by some of the state’s largest health insurers will go up starting today. The rate increases, which were expected, mostly affect policyholders in plans offered through small businesses. Depending on the plan and the carrier, hikes will average from 3 percent to more than 17 percent, but some individuals within the plans could see much higher jumps. An unknown number of Aetna’s small-group customers will take a wallop, with rates soaring 92.5 percent, according to California Department of Insurance data. The average increases for Aetna small-group customers in the two plans affected are 12.7 percent and 17.4 percent.