Breakers in a 30 amp panel

I have a 30 amp panel in my garage with a 2pole 30amp main breaker. The panel is fed from another 2 pole 30 amp breaker located next to my electrical meter. I have 3 15 amp breakers in the panel running 3 outlets and 2 sets of lights. Can I install a 30 amp breaker in the panel to install and RV outlet?