Sterling Construction (STRL) had the best month in 2015 by a large-cap US stock in March 2015, returning 64.4%.

ASSET	MONTH	% RETURN
Sterling Construction (STRL)	March 2015	64.36%
Harmony Gold Mining (HMY)	January 2015	63.16%
Harmony Gold Mining (HMY)	December 2015	60.34%
Exelixis (EXEL)	July 2015	59.17%
Amkor Technology (AMKR)	February 2015	53.23%
Petroleo Brasileiro Petrobras SA ADR (PBR)	April 2015	52.49%
Exelixis (EXEL)	February 2015	50.26%
Nebius (NBIS)	October 2015	49.21%
Neurocrine Biosciences (NBIX)	January 2015	49%
Flutter Entertainment (FLUT)	December 2015	48.86%
Trip Group Ltd ADR (TCOM)	October 2015	46.59%
AngloGold Ashanti (AU)	January 2015	45.14%
Vale SA ADR (VALE)	April 2015	41.88%
Alibaba (BABA)	October 2015	40.89%
Trimble (TRMB)	October 2015	40.87%
First Solar (FSLR)	February 2015	39.98%
Dycom Industries (DY)	February 2015	39.86%
Lumentum (LITE)	November 2015	39.37%
Sterling Construction (STRL)	November 2015	39.03%
Agnico Eagle Mines (AEM)	January 2015	38.42%
Lattice Semiconductor (LSCC)	November 2015	38.24%
YPF Sociedad Anonima (YPF)	October 2015	38.16%
Amkor Technology (AMKR)	October 2015	37.61%
Kraft Heinz (KHC)	March 2015	35.8%
Baidu (BIDU)	October 2015	35.53%

Large-cap stocks are treated as having a market cap of $10B+.