I've yet to see an argument where you simply MUST get that +3 to your main stat, for RP, while a +2 is just utterly unacceptable.
Orc Wizard He was cloistered and very educated. But mechanics gives him a 13, +1. Only average~above average. Him being really smart and scholarly is already failing. Should be a competent wizard, but a +1 is very far behind a +3 so he seems to others to be very weak, especially cause he only ever missed.
So my roleplay as a Orc Wizard, someone who isn't brutish and is supposed to be quite smart and competent in his own right, got boiled down to me failing and people noting that I was just bad at being both an Orc and a Wizard. Mechanics and character concept could not match. A competent character should only miss a few times a session, but a combination of bad luck and low stats meant I failed every kind of check related to my PRIMARY stat.
DnD is a roleplaying game. You want both roleplaying and game, and both are connected. Without one the other does not stand as well. Yes too strong or too minmaxed of a character can break RP but so can too weak of a character. I was able to roleplay initially but the game part breaking down meant the RP broke down. On another character, an aasimar celestial warlock, I was able to roleplay very effectively as a healer because mechanically I had that and
TLDR; Because DnD is a roleplaying game, both halves are important and contribute to eachother. Tasha's makes it easier to have a balance.
You can have a 15, I dont know where you source your information from.
Orc Features Source: Volo's Guide to Monsters Ability Score Increase. Your Strength score increases by 2 and your Constitution score increases by 1.
Check your Errata.
Orc Traits (p. 120). In the Ability Score Increase trait, the text has changed to read “Your Strength score increases by 2 and your Constitution score increases by 1.” The adjustment to Intelligence has been removed.
