"Final" Edition: 2015 Open Enrollment Period vs. 2014
2018 MIDTERM ELECTION
Time: D H M S
Important: Technically this is not the "final" comparison of 2015 (full year) vs. 2014 (full year), since there's still the upcoming "Tax Season" enrollment period, along with additional enrollments/policy cancellations throughout the rest of the year via qualifying life events (marriage, divorce, giving birth, losing/gaining a job, moving to a new state, etc).
However, in terms of the 6-month-plus-2-week 2014 period and the 3-month-plus-1-week 2015 period, this is as close as I can get to an apples-to-apples comparison.
The HHS Dept. projected roughly a 30% enrollment increase this year (10.4 million QHP selections, 9.1 million actual paid enrollments). I projected roughly a 56% increase (12.5 million selections, 11.0 million paid).
In the end, it split the difference towards the high end: Over 11.7 million selected, of which around 10.3 million either have or are about to pay for at least their first monthly premium. This corresponds to roughly a 46% increase over 2014.