It will be OK for year, nevermind 45 minutes. I don't recommend trying this during a party when everyone is drawing off the keg, but as long as you're not trying to pour, it's fine.
as long as the seals on the poppets, posts, and main hatch are good - if it was holding pressure before hand, then the carbonation will last for a very long time. think of the keg like a really big bottle - you put your beer in the bottle, put on the cap. the carbonation stays in there.