If '$\text{P}$ ' represents '$÷$ ', '$\text{Q}$ ' represents '$\times$ ', '$\text{R}$ ' represents '$+$ ' and '$\text{S}$ ' represents '$-$ ', what is the value of the mathematical expression $9\text{Q}15\text{P}3\text{R}8\text{S}5$?

Substitute the given operators into the mathematical expression $9\text{Q}15\text{P}3\text{R}8\text{S}5$:
$$\text{Expression}=9\times 15÷3+8-5$$

Applying the rules of $\text{BODMAS}$ (Division first, then Multiplication, Addition, and Subtraction):

1. Division: $15÷3=5$

$$\text{Expression}=9\times 5+8-5$$

2. Multiplication: $9\times 5=45$

$$\text{Expression}=45+8-5$$

3. Addition: $45+8=53$

$$\text{Expression}=53-5$$

4. Subtraction: $53-5=48$