Applied Digital (APLD) had the highest return between 2014 and 2015 by a mid-cap US stock, returning 600%.

ASSET	YEARS	% RETURN
Applied Digital (APLD)	2014-2015	600%
Green Brick Partners (GRBK)	2014-2015	510.53%
Celsius (CELH)	2014-2015	397.46%
CleanSpark (CLSK)	2014-2015	350%
Amicus Therapeutics (FOLD)	2014-2015	312.77%
Pampa Energia SA ADR (PAM)	2014-2015	288.47%
RadNet (RDNT)	2014-2015	267.86%
Globant (GLOB)	2014-2015	223.36%
TG Therapeutics (TGTX)	2014-2015	201.26%
Transportadora de Gas del Sur SA ADR (TGS)	2014-2015	185.92%
Skyworks Solutions (SWKS)	2014-2015	175.89%
BBVA Banco Frances SA ADR (BBAR)	2014-2015	174.99%
Agios Pharm (AGIO)	2014-2015	173%
Travere Therapeutics (TVTX)	2014-2015	168.29%
JetBlue Airways (JBLU)	2014-2015	164.6%
Grupo Financiero Galicia SA ADR (GGAL)	2014-2015	158.98%
Qorvo (QRVO)	2014-2015	148.05%
Banco Macro SA B ADR (BMA)	2014-2015	145.31%
Ultragenyx (RARE)	2014-2015	144.93%
Silicon Motion Technology (SIMO)	2014-2015	133.32%
EPAM Systems (EPAM)	2014-2015	126.05%
Manhattan Associates (MANH)	2014-2015	126.01%
Patrick Industries (PATK)	2014-2015	125.7%
Alaska Air (ALK)	2014-2015	124.47%
LeMaitre Vascular (LMAT)	2014-2015	121.74%

Mid-cap stocks are treated as having a market cap between $2B and $10B.