The first half of the year saw a 20% growth in the market, as sales reached $2.8 billion compared to China's figure of $1.89 billion. Source:

Both the strength of the dollar and the introduction of the Droit de Suite (artist's resale rights) in the EU meant that a lot of important artworks were sold in America as of London.

Preview of Christie's spring sales in New York of Impressionist, Modern, Post-War And Contemporary Art, London, Britain - 10 Apr 2015 Picasso's The Women of Algiers (Version 0)
Image via the Telegraph

Two artworks which contributed enormously to the US taking the lead was Picasso's The Women of Algiers (Version 0) which sold at Christie's for a staggering $178 million and Giacometti's Pointing Man sculpture which broke records as the most expensive sculpture to be sold at auction when it sold at Christie's for $140.6 million.

stream_img Giacometti's Pointing Man
Image via ITV

The UK continues to see growth in the market, as sales were up by 6% in the first 6 months of 2015, with sale room figures totalling £1.2 billion ($1.9 billion.) Source