CI3: Apache vs Lightspeed Server

Hi to all developers...
I've read some posts that said running an app on linux with Apache server is not good and efficient and maybe slow when visitors will being more and more. Now I've developed a web-based application that in part of it, there is an online exam. The raw script is not so large or complex; get questions from database and show to users and they register answers  in a defined time.

My question is: when many users (500-1000 or maybe more) want to take part in online exam, or generally, many users want use different parts of the app at the same time, is the lightspeed server really better option than apache? Is it better that I buy a web host with lightspeed server for more performances and...? What is the real and in action difference between them?
I read some post about differences between them, but those did not help!

thanks for attention and especially thank for experts and who are skilled and want to share info.