Verification of Sallen Key Design
With equal values for both resistors and capacitors, the Q of the circuit is 0.5. At the natural resonant frequency of 2nd order filters, the Q value is the magnitude of the transfer function. So, at 159.15 Hz, the magnitude of the transfer function is half or down 6 dB. I expect that at around 100 Hz, the magnitude of the transfer function is down 3 dB.


  Another design specification is that R1=R2 and C1=C2.


This will always mean a Q factor of 0.5 (critical damping = 1) and so, you would have to reduce both capacitors to produce a higher natural resonant frequency in order to get a 3 dB point at 150 Hz. It's the same for an RLC low pass filter too: -



In the design I've chosen R = 200 ohms, L = 100 mH and C = 10 uF to achieve a natural resonant frequency of 159.15 Hz and a Q of 0.5. In the upper graph I've position the cursor at 159 Hz and you can see that the magnitude of the transfer function is -6 dB.

In the lower graph I've moved the cursor to around 100 Hz and revealed that the magnitude is more like -3 dB.

Pictures from this interactive tool.