I would say over 15 % of the people would
A maximum of 15%. Bitcoin is not a very stable currency and panic can screen out many users from using this currency. In addition, with the increase in operations, delays are possible.
This percent of your prediction maybe will in this 2018 only if you can see bitcoin price from other country are increasing that much too, Which is they had so much operations happening inside there country we wouldn't know what is it but maybe half of the wold will implemented bitcoin as there secondary currency.
If bitcoin will grow in such a fast-paced manner, then it is quite possible. It all depends on the activity of users because they are held by this currency.