Partners HealthCare’s chief executive, Dr. David Torchiana, topped the list of executives at the state’s largest nonprofit hospitals who received sizable pay raises in 2015, according to their most recent public filings. Torchiana, who oversees the state’s largest health system and largest private employer, earned nearly $4.3 million in total compensation. That includes a base salary of about $1.9 million, plus bonuses and retirement benefits.