First, China population is 1.38 billion now, rather than 1.5 billions as you said.
Second, China per capita electricity producton was 4100 kwh in 2014, much higher than what you think, and higher than most of the nations in the world.
Third, purification of nuke materials needs lots of energy (electricity), and China used only parts of electrictiy in manufacturing section even though China's physical GDP in 2015 was bigger than the sum of G7 countries combined!
Fourth, where are the other portion of energy gone in China? An explanation is that was used to produce nuke materials - that translate to the conclusion that China has more than 1000 nuke warheads!!!