This sounds like more a question of interpretation than of mathematics, but my intuition is to take the logarithm of everything. So, if the parameters in one quarter were $s_1 = a_1b_1c_1$ and those in the second quarter were $s_2 = a_2b_2c_2$, then we can also write
$$
\log s_1 = \log a_1 + \log b_1 + \log c_1 \\
\log s_2 = \log a_2 + \log b_2 + \log c_2
$$
and you should find that the percentages are easier to define. For instance, with your $2014$ numbers, from the first quarter to the second, we have
$$
\log 100 = \log 1000 + \log 0.1 + \log 1 \\
2 = 3 + (-1) + 0
$$
as compared to
$$
\log 150 = \log 1500 + \log 0.2 + \log 0.5 \\
2.176 = 3.176 + (-0.699) + (-0.301)
$$
The log of the total sales went up $0.176$, of which increase in customers accounted for $0.176$, increase in conversion accounted for $0.301$, and increase (negative) in sales price accounted for $-0.301$. The percentage breakdown would be increase in customers representing $100$ percent, increase in conversion representing $301/176\cdot 100 \doteq 171$ percent, and increase (negative) in sales price representing $-171$ percent.
A scenario where each component accounted for a positive increase would be as follows. Suppose that in the second quarter, we instead had
$$
\log 210 = \log 1250 + \log 0.12 + \log 1.4 \\
2.322 = 3.097 + (-0.921) + 0.146 \\
$$
In this case, we would have an increase in log sales of $0.322$, of which $0.097$ came from customer count, $0.079$ came from conversion, and $0.146$ came from sales price, resulting in a percentage split of approximately $30$, $25$, and $45$ percent, respectively.
EDIT: I fixed the numerical values in the second example, some of which were in error. Sorry about that!
Best Answer
The percentage of the goal achieved under the same definition as increasing something, actual/goal, should be similar in some ways when going the other direction.
The following equation determines the percentage of the goal that is overshot or undershot depending if it is positive or negative.
$\frac{goal-actual}{goal}$
This essentially finds the difference between what you achieved and what you aimed for and turned it into a percentage of overshooting or under shooting the goal.
Obviously you need to add 100% (or 1) in order to find how much you achieved instead of how much you overshot or undershot the goal.
Using the same example, reducing the debtor days to 90 with the intended goal of 100 days results in $\frac{100-90}{100}+1$ = 1.1 or 110% of goal achieved.
In fact, the original equation your provided, $\frac{actual}{goal}$ is actually the same one I just wrote but in reduced form and with the numerator changed a little. Using my method of finding percentage overshot, and adding 100% to find % goal achieved it would have been $\frac{actual-goal}{goal}+1$, which reduces to $\frac{actual}{goal}-1+1$, finally achieving the equation $\frac{actual}{goal}$