I'm not sure if using an app is a good idea to improve load speed. It'd be better if you can have a technical guy to check your page and manually do the task.
Basically, improving load speed will involve:
Install lazysize script (https://github.com/aFarkas/lazysizes) and update image source in the theme
Use proper image size for each device:
Check the container size
Use img srcset instead of src, one for retina and one for non-retina screen
Remove unused CSS and unused JS in the theme's asset folder
Remove unused apps
Optimize, Minify code:
Minify HTML code by adding this code into theme.liquid file https://pastebin.com/raw/V9gRwnWR
Concat, minify all CSS files and load them inline inside <head> tag
Concat, minify JS files and load them at the bottom of the page (before </body> tag)
Add font-display: Swap into all external fonts
=> TL,DR: I suggest you have a technical guy to do it manually, you can either follow the above steps, or read this article about how to optimize your page speed.
Welcome to Shopify, if you are facing slow load times can be due to many factors, Apps, Images, Videos, Back links and more
you can search on Shopify Marketplace for an App, keep in mind that sometimes the App may clash with another Apps you installed. that is why we recommend having a deep look ant the theme code to look up what cause the slow load.
do not hesitate to contact us
No, you cannot improve site speed with more apps. On the contrary, you should remove unused or repeated apps that affect the site rending. You can use google pagespeed insight to have a quick check: https://developers.google.com/speed/pagespeed/insights/