In fact, the problem you are encountering now is normal, and this is the "pain" that everyone will encounter. Think about it, the original writing posture and pen holding posture have become accustomed to it. It is a painful process to change the original habit by learning calligraphy now. Don't be afraid of this process and don't give up halfway.
There is no shortcut to speed up. Only by persisting in practice and perseverance can we develop a beautiful hand and speed up quickly.
Wish you success!