Let's simplify the given expression step by step:

Step 1: Simplify the terms inside the parentheses first.
[ - 3\frac{1}{5} a ^{8} b - ( \frac{1}{2} a ^{3} b^{8} )^{4} = - \frac{16}{5}a ^{8} b - \left( \frac{1}{16}a^{12}b^{32} \right) ]

Step 2: Simplify the second term within the parentheses.
[ \frac{1}{16}a^{12}b^{32} = \frac{a^{12}b^{32}}{16} ]

Step 3: Evaluate the expression within the parentheses.
[ - \frac{16}{5}a ^{8} b - \frac{a^{12}b^{32}}{16} = - \frac{16}{5}a ^{8} b - \frac{a^{12}b^{32}}{16} ]

Step 4: Simplify further using the power rule.
[ - \frac{16}{5}a ^{8} b - \frac{a^{12}b^{32}}{16} = - \frac{16a ^{8} b}{5} - \frac{a^{12}b^{32}}{16} ]

Step 5: Evaluate the final expression.
[ - \frac{16a ^{8} b}{5} - \frac{a^{12}b^{32}}{16} ]

Now, let's move on to the second part of the expression:
[ (0.6 \times {5}^{3} - 15)^{2} = (0.6 \times 125 - 15)^2 ]
[ = (75 - 15)^2 = 60^2 = 3600 ]

Therefore, the simplified expression is
[ - \frac{16a ^{8} b}{5} - \frac{a^{12}b^{32}}{16} + 3600 ]