Bitcoin transactions per day more than doubled; Bitcoin became more global; Bitcoin volatility decreased; The price of bitcoin went up; The Bitcoin developer ecosystem grew
Here are a few major events to keep an eye on in 2016: An emerging application layer for Bitcoin. In 2015 the infrastructure layer of bitcoin matured. With better developer APIs, the 21 Bitcoin Computer enabling a new group of bitcoin applications, and open source communities like Blockstack flourishing, we expect bitcoin applications to start to take off in 2016. The next bitcoin halving occurs in July. Currently, 25 bitcoin are created every 10 minutes (meaning that for the price to hold constant, there needs to be net buying activity of roughly 3,600 bitcoin per day). In July 2016, the mining reward will cut in half and only 12.5 bitcoin will be created every 10 minutes. This may cause the price of bitcoin to increase.
https://blog.coinbase.com/2015/12/31/2015-bitcoin-year-in-review/