If a person has a 15:1 head vs. a 12:1 head will their compression psi be higher like 180 vs 150psi?
And can a person use this psi. to determine what fuel to use?
The reason I ask is I have a 12:1 cool head from Aaen and its been resurfaced a couple times so I'm sure its a little higher now. Thank you very much.

 

The hpd 15:1 head has around 170-175 cranking compression ratio. I don't know for sure, but I'd say the 12:1 is around 145-150 cranking (static) psi. You can use static compression as a guide the 15:1 dome you'll need about a 108 motor octane which is around a 112 mr2 which is what you would see on the pump rating.

 

If in the same engine with the same camming, Yes.
No, not really. Octane rating is determined by many factors, not just compression ratio. There is altitude, ignition timming, intake air temp, combustion chamber shape and many, many more things.
Like POLARISFREAK said, you can only use compression as a guide. You need to learn to read your plugs for signs of detonation and sneak back to a lower octane fuel.