MOSCOW, Nov 21 (Reuters) - Russia will build six major chemical plants by 2015 as it seeks to cut imports of value added products, including plastics, for booming industries such as the car sector, a minister said on Wednesday. Energy and Industry Minister Viktor Khristenko said the government wanted the share of the chemical industry to rise to 3 percent of gross domestic product by 2015, from 1.7 percent now, under a strategy reviewed at a cabinet meeting.