looking to save some gas and need help getting my cal right or just a different one entirely currently getting under or around 15mpg with premium

i only want to run like 7psi and use standard 87 gas no racing .etc

1990 sbec- garret turbo stock 2.2l t2 , 3bar, +20 injector, large fmic, ported 2pc, ported exhaust, 3" exhaust/downpipe, 2.5 sv, 255 pump, upgrade fuel rail. 52mm tb

can anyone help me out? i have a cal to use as a base that runs good but its more for performance and idles very rich at times