In SpeedFan you can offset the sensors to get a 'correct' reading. Since it's widely believed that Speedfan is off by -15c, you need to offset all the core temp readings by 15c.

Click on 'Configure', then the 'Advanced' tab. Select 'INTEL CORE' from the dropdown list, now select each temperature in turn and choose an offset of 15. Tell Speedfan to remember it.



Your temps will now display correctly