I'm not in your jurisdiction, but my son had the same kind of thing happen when he was your age and his friend was 17.

They didn't try to run, so they weren't quite as hard on them.

He ended up pleading no-contest so he didn't have to go through ASAP (the drug & alcohol program) - the charges were reduced to just paraphalia, he got 30 days suspended, and that was that. If he was willing to do the classes & get tested for a year, he could have cleared his record.

Here's a few legal points for you - as I understand them (I'm not a lawyer)

Contrary to public opinion, they do not have to mirandize you. However, if they don't, it can mean that some things you say "may not" be admissable.
Best course of action is to never say anything until you talk to a lawyer - even if that means you go to jail.

If they smelled pot, that's probable cause & reason enough for a legal search.

As far as the arrest, as soon as you feel like you're no longer free to go, most lawyers will argue that you're arrested at that time.
I'm not sure that they have to tell you what you're charged with right away.

If you want to know how things turn out in the Utah courts, go to court & watch for a few hours.
It's free to the public and you'll know what you're facing. Some states also have court cases & verdicts in an online database that you can search.
I'm betting you don't do any jail time, but everything else is a definite possibility.

Have you talked to a lawyer?

They're trying to scare you with all those charges because you guys tried to get away. I bet a lot of them - like the contributing - get dropped.