Most exercise front-loads the hard part while you are fresh. A slow class does the opposite: the deepest, longest-held shapes land in the last third, after forty-odd minutes, when you might assume you have least left to give.
Tissue behaves differently once it is warm
A cold muscle resists lengthening — pull on it and it pulls back. A muscle that has spent half an hour moving gently yields instead. That is not a mood, it is mechanics: connective tissue is more pliable once it has warmed and softened, so the same forward fold that stops at your knees at the start can reach the floor by the end.
So the sequence is built as a curve. The early part warms the body from the inside — no heated room, just movement and breath — so that the later shapes are available at all. Ask for them in the first ten minutes and you would only find the cold limit, and maybe a strain.
What this means for you
Two things. First, do not judge the class by how you feel at minute fifteen — that is not where it is going. Second, do not skip the beginning to “get to the good bit”. The beginning is what makes the good bit possible.
It is the whole argument for a slow practice in one line: warm first, then reach.