The formulation you quoted is not clear - the problem is not in the grammar of if, but in the misused vocab. Your formulation where you explained what you meant:
since the question is simple enough I wish to get answered as quickly as possible
while rather blunt and not exactly polite is far easier to understand.
It is not really a matter of language, but I don't think that there is a polite way to say: This is an easy question, so the answer should not take too long. The first part makes it impolite, because you are assuming what is easy/difficult for the person who has to answer and what's more that they should make your question a priority.
To be polite you can omit the first part and nicely ask for a quick response. For example:
I would really appreciate a quick (an urgent) response.
Another way is to state that you are in a hurry for some reason (specified or unspecified) a for example:
This matter is urgent for me (because...), can you please respond quickly?
Don't forget that a thank you goes a long way.
You might also find these options from Merriam-Webster useful.