Do caster out of combat options matter?

[Doug Lampert]

Can you clarify what you mean by that? Sorry, I don't quite get what you mean when you say there is no such thing as a skill check.

I'm not stoutstien, but, in 5th edition there are three types of rolls, ability checks, saves, and attacks. Some rolls of each of these types get to add the character's proficiency modifier.

There is no such thing as a skill check. It simply does not happen in the rules.

There are ability checks where you get a bonus of being allowed to add your proficiency modifier because you have a relevant proficiency.

The baseline values for "how hard is this ability check" should be set based on the ability scores characters are likely to have. Any added bonus from proficiency is a bonus and should make success more likely rather than making you increase the DC to compensate. When figuring a DC, 15 is "the best in the world succeed at this on a roll of 10 or higher without a special bonus", because proficiency is a special bonus to an ability check, and this is an ability check, not a skill check.