Complex sentence: In 2015, Pew Research estimated that 1% of the U.S population self-identify as PC (USA), and in 2012, when all members were included, the denomination reported 2.8 million total.
Split into simpler sentences: In 2015, Pew Research estimated that 1% of the U.S population self-identify as PC (USA). In 2012, when all members were included, it was reported to have 2.8 million total.