Has your manager actually told you you aren't delivering fast enough? Or is that just a perception you have?

If you're not involved in the sizing or estimation then don't commit to any dates and don't bow to any pressure over dates.

In my experience pressure to deliver fast is never enforced. It's all talk used to squeeze and bully people and by incompetent managers who don't know any other knob to turn. Consider this a psychological game. Don't play into it. If you don't deliver by the dates chosen by your manager nothing will actually happen.

In my career whenever I've been faced with the choice between speed and quality I have always regretted it. Even when managers and everyone around me said otherwise. I have never, not once in my 20 year career, actually been punished for good quality even if that meant being late.