Maybe another way to look at the situation is absolute pressure. 0 being a total vacuum, 14.7 psi is normal atmospheric pressure at sea level, 30 psi (14.7 plus 15.3 psi boost) about two atmospheres of pressure. Horespower will rise about the same as absolute pressure, if the efficiency of the blower/intercooler is high enough.
The valve lift can remain the same, heads can remain the same, the extra pressure will put more air in the cylinder.