To solve this problem, we need to follow the order of operations (PEMDAS - Parentheses, Exponents, Multiplication and Division from left to right, Addition and Subtraction from left to right).

First, let's simplify the expression inside the parentheses:
0.8 + 2/3 = 0.8 + 0.6667 ≈ 1.4667

Now, let's simplify the division inside the parentheses:
1.4667 ÷ 3 2/3 = 1.4667 ÷ (11/3) = 1.4667 * (3/11) ≈ 0.4012

Now, let's subtract the result from the division inside the parentheses from 15/64:
15/64 - 0.4012 = 0.2344

Finally, let's calculate 320% of 0.2344:
320% * 0.2344 = 3.2 * 0.2344 = 0.75008

Therefore, the final answer is approximately 0.75008.