1. It is fifteen past three.

Question

2. It is fifteen after three.
3. It is a quarter after three.
4. It is three quarters after/past two.
(Are they all the same and grammatical?)

5.It is ten before three.
6. It is ten minutes before three.
7. It is ten minutes before three p.m.
8. it is ten minutes before three o'clock.
9. It is ten before three p.m.
(Are they all grammatical? Which ones are not used?)

Answer 1

All are grammatically correct, but not all are commonly used.

These are the uncommon ones:
4, 9