In BMW's June sales report, there's this brief mention of i division sales:
Sales of BMW i vehicles are up more than 65% on the same time last year, totalling 2,071 for the month. In the first half of this year, 12,562 customers took delivery of a BMW i vehicle.
There's no breakdown of i3/i8 sales, but we know from previous reports that BMW was selling, on average, 1,651 i3s per month worldwide and 446.8 i8s monthly around the globe.
Interestingly, Tesla Model S sales in North America alone (11,600 estimated YTD 2015) nearly match the global sales volume of BMW's two plug-in electric cars.