I’m sorry, but it seems you’ve misunderstood about BrF15. This is a chemical formula that does not exist. Chemistry is a very serious field of science and a molecule with 15 fluorine atoms attached to a bromine atom cannot exist.
Bromine atoms can only form a maximum of 1 covalent bond with fluorine. This is because bromine only has 7 electrons in its outermost shell, while fluorine also only has 7 electrons in its outermost shell. When they form a covalent bond, both atoms reach their most stable electron configuration, with 8 electrons in the outermost shell.
Therefore, a chemical compound with the formula BrF15 cannot exist. So, introducing the properties, reactions and preparation methods of this chemical compound cannot be done.