NEW YORK & LONDON--(BUSINESS WIRE)--WPP (NASDAQ:WPPGY) today reported its 2015 Interim Results. Key figures             £ million     H1 2015   ∆ reported1   ∆ constant2     H1 2014   Billings     23,156   5.0%   5.0%     22,060   Revenue     5,839   6.8%   6.4%     5,469   Net sales     5,041   5.2%   4.7%     4,792   Headline EBITDA3     782   6.7%   6.7%     733   Headline PBIT4     669   7.6%   7.9%     622   Net sales margin5     13.3%   0.36   0.46     13.0%   Profit before tax     710