How long does it take you?

I've had gobs of orgasms on my own before, but I've never been able to have one with someone else, whether via sex, oral, or fingering. I've only had sex with one guy and only five times with him. He's had sex with two other people before and has been able to make them cum fairly quickly. Could it just take me a long time? He usually only lasts up to about fifteen minutes, and doesn't really do any direct clitoral stimulation unless we're just fooling around and not actually having sex. I'm tired of faking when his arms get tired! Any tips?