Hi Zechris,
This is a puzzler. On the face of it your boot times should have been about the same, perhaps a tad faster. How is the 970 Evo attached? Have you installed the Samsung driver? have you made any other changes? How did you transfer the OS from the 850 to the 970 Evo? How much slower is the boot time?
More questions than an answer
Regds, JR