I think it's pretty awesome to have both Jason Day and Jordan Spieth right now. But we're talking about Player of the Year, not Player of the Final 6 weeks of the Season. You have to start with the Majors, and there Day has not been in the same league with Spieth in 2015. If they'd both won 2 majors, then I'd say Day has been Player of the Year. But with Jordan winning two, Day winning one, and Spieth's record in the two he didn't win far superior to Day's record in the ones he didn't win ... well, you have to do some sort of gymnastic math to claim Day has been Player of the Year.
Sure wish I could watch the Tour Championship but, unfortunately, PGA Tour Live is "having technical issues" and their live stream isn't working.