pinning glutes is much harder than pinning ventro glute. ventro glue is on the side but isn't down on the thigh.... it is a big, thick muscle that can hold lots of volume if necessary. you shouldn't need a 1.5inch pin, i also pin with either 1/2 inch, 5/8, or 1 inch, and always using 25g or smaller. slins if the volume of compound is low enough.
i recommend you spend a few bucks and grab some new needles. and i recommend you learn how to inject VG. it's basically down a bit below the obliques..... super easy to reach, can pin with both hands either side..... far easier than straight in the ass. you can shoot it sitting, standing laying down, whatever, you don't need a mirror to feel better doing it. i mean.... aside from at first feeling weird about knowing exactly where to pin, there pretty much isn't a downside.