If I have a base Charisma level of 10, does temporarily bolstering it above and beyond that with suits or chems have any kind of positive impact on Charisma Checks or from a calculation standpoint does it treat a Charisma value of 15 the same as a Charisma value of 10?
In general, boosting stats past 10 still helps. This can be directly observed with most stats, and most easily with Strength: increasing your Strength past 10 continues to improve your carrying capacity. You can find more on this in the answers to the question: Can SPECIAL stats be increased past 10?
However, unlike your carrying capacity, you cannot directly observe your chance to succeed on a persuasion attempt. It's possible that you already have 100% chance to succeed on persuasion attempts at 10 Charisma. Iszi asks about this in the question: How does Charisma affect your negotiation skills?
But Not Enough to Matter
A few of us recall failing a check at 10 Charisma, but didn't keep a record of it. Even if we recall correctly, it was only once or twice ever. Iszi claims to have never failed a persuasion attempt with a character that started with 10 Charisma. So, once you get past 10, it might help, but not enough to really matter.
This is especially true if you don't mind loading and trying again. In that case, what's the difference between a 98% chance and a 100% chance?
I definitely failed a persuasion check with 10 Charisma last night. I was talking to the Alpha of the Pack in Nuka-World, Mason. There is a red check to tell him to be a "good dog". I failed that one.
I recorded a video of it with my Xbox One DVR. I'll link to it once I figure out how to upload it.
This is the first time I've failed a check with 10 Charisma since I first answered this question, seven months ago. I've played through the game multiple times since then, so it's extremely rare.