The 1.5 V had to come from somewhere. I prefer to go right to the source.Page 11
of the 2nd Generation Intel Core Processor Family Desktop Datasheet
Section 1.2.1 System Memory Support DDR3 I/O Voltage of 1.5 VPage 80 - Table 7-6. Processor System Agent I/O Buffer Supply DC Voltage and Current Specifications
VDDQ - Processor I/O supply voltage for DDR3Minimum: 1.425 V
Typical: 1.5 V
Maximum: 1.575 V
Couldn't be any clearer than that.