Customize queries in mysql with php 7 and ajax calls

I need somebody to customize some queries that leave the operation of my web application slow like the requests in ajax and freeze the screen, in this application I use php 7. Note: I get more slow in the application when I use wampserver in windows, and in linux the slowness is a little smaller. I want to use this web application on both windows with wampserver and linux on cloud server. Note: I am a php developer, and along with another freelancer, I have developed the application and the queries. Note: I believe that there will be only two files to be adjusted, one that structures the display of the php page and another that handles the queries and requests in ajax. Note: this web application must be customized and tested in windows environment using wampserver, I get to pass the files later. Note: necessary deep knowledge in mysql.