To calculate the tip, you can use the following formula:
\[ \text{Tip} = \text{Bill Amount} \times \text{Tip Percentage} \]
In this case, the bill amount is $150 and the tip percentage is 15% (or 0.15 when expressed as a decimal).
\[ \text{Tip} = 150 \times 0.15 = 22.5 \]
So, the tip is $22.50.
Next, to find the total amount they will pay, you add the tip to the bill amount:
\[ \text{Total Amount} = \text{Bill Amount} + \text{Tip} \]
\[ \text{Total Amount} = 150 + 22.5 = 172.5 \]
Therefore, the tip is $22.50, and the total amount they will pay is $172.50.