Financial report context:
in 2017 , the company granted 440076 shares of restricted class a common stock and 7568 shares of restricted stock units . restricted common stock and restricted stock units generally have a vesting period of two to four years . the fair value related to these grants was $ 58.7 million , which is recognized as compensation expense on an accelerated basis over the vesting period . dividends are accrued on restricted class a common stock and restricted stock units and are paid once the restricted stock vests . in 2017 , the company also granted 203298 performance shares . the fair value related to these grants was $ 25.3 million , which is recognized as compensation expense on an accelerated and straight-lined basis over the vesting period . the vesting of these shares is contingent on meeting stated performance or market conditions . the following table summarizes restricted stock , restricted stock units , and performance shares activity for 2017 : number of shares weighted average grant date fair value .

Financial table:
number of shares: outstanding at december 31 2016; weightedaveragegrant datefair value: 1820578; column_3: $ 98
number of shares: granted; weightedaveragegrant datefair value: 650942; column_3: 129
number of shares: vested; weightedaveragegrant datefair value: -510590 ( 510590 ); column_3: 87
number of shares: cancelled; weightedaveragegrant datefair value: -401699 ( 401699 ); column_3: 95
number of shares: outstanding at december 31 2017; weightedaveragegrant datefair value: 1559231; column_3: 116

Additional report context:
the total fair value of restricted stock , restricted stock units , and performance shares that vested during 2017 , 2016 and 2015 was $ 66.0 million , $ 59.8 million and $ 43.3 million , respectively . under the espp , eligible employees may acquire shares of class a common stock using after-tax payroll deductions made during consecutive offering periods of approximately six months in duration . shares are purchased at the end of each offering period at a price of 90% ( 90 % ) of the closing price of the class a common stock as reported on the nasdaq global select market . compensation expense is recognized on the dates of purchase for the discount from the closing price . in 2017 , 2016 and 2015 , a total of 19936 , 19858 and 19756 shares , respectively , of class a common stock were issued to participating employees . these shares are subject to a six-month holding period . annual expense of $ 0.3 million for the purchase discount was recognized in 2017 , and $ 0.2 million was recognized in both 2016 and 2015 . non-executive directors receive an annual award of class a common stock with a value equal to $ 100000 . non-executive directors may also elect to receive some or all of the cash portion of their annual stipend , up to $ 60000 , in shares of stock based on the closing price at the date of distribution . as a result , 19736 shares , 26439 shares and 25853 shares of class a common stock were issued to non-executive directors during 2017 , 2016 and 2015 , respectively . these shares are not subject to any vesting restrictions . expense of $ 2.5 million , $ 2.4 million and $ 2.5 million related to these stock-based payments was recognized for the years ended december 31 , 2017 , 2016 and 2015 , respectively. .

Question: in millions , how much compensation expense was attributable to directors in the years ended december 31 , 2015 through 2017?
Answer: 7.4