I’d missed this when it came out. Gallup does regular interviews and keeps track of the religion of people who respond to their polls. For 2015 that was 174,000 people. Their rate for Mormons was 2% compared with Christans at 75.2% and Nones at 19.6%. This is significantly higher than Pew (1.6% Mormon; 70.6% Christian; 22.8% None).