30 amps
There are two circuit breakers to consider. The first is the one mentioned by Clodhopper and is located on the power pedestal. If you are using air conditioning and wish to use a microwave, you most likely will not be able to run someone's deep freeze at the same time. But the real test is, what is the current draw of the freezer and also what is it's duty cycle, since the amount of time that it will operate is just as important.
But there is also a second circuit breaker involved, in your RV. The 120V distribution panel has circuit breakers that supply different things in the RV. Your outside outlet is only one of the outlets that is supplied by one 15A circuit breaker. If the total of everything you have plugged into that circuit should exceed 15A, it will open. In fact, circuit breakers are only designed to carry 80% of that rated load on a constant basis.
The suggestion to plug directly to the power pedestal is a good one, if the 15A outlet there is connected to a different leg of the power than your 30A outlet. Very often it is on the same circuit breaker due to limitations of the RV park wiring. Is everyone planning to stay in one RV site? If some of your friends get a site of their own, why could you not plug that freezer into it? I don't know of any RV park or public park that does not have a limit on how many people can stay in one site. I suggest that the owner of the freezer get a site and plug into that.