This magazine holder holds 2 15rd Glock 23 and G27 .40S&W magazines just fine. The fully loaded magazines sit in there tight and require a decent amount of pull to remove them from the holder. They aren’t terrible bulky, and I can’t see how they could be anymore compact given the weight they have to be able to carry.
https://www.amazon.com/Magazine-Holder-Holster-Ultimate-Caliber/dp/B014L6JFEA

