Advertising

As far as I know, every network advertises as much or as little as they see fit.

Too much advertising though and they will lose viewers. People tune in to see content after all, not to watch ads. The number of ads is probably regulated by whatever the marketplace will sustain.

Probably. I think there is one network that is nothing but advertising/informationals.

For broadcast television, it's about 15 minutes.

Television advertising is the sending of promotional messages or media content to one or more potential program viewers. The viewers are influenced by the messages which results in actions that benefit the advertiser.