Gtmetrix shows 6.2 seconds but waiting time 20 seconds

I have an ecommerce website in wordpress. its Gtmetrix score B(89%) and shows "fully loaded time" of 6.2 seconds but website loads almost in 20 seconds. Screenshot is here https://prnt.sc/mu11kw and this is watarfall https://prnt.sc/mu13id Over 95% of the time it takes to load the page is "Wait" time as shown in the this screenshot. https://prnt.sc/mu0zgd

on the other hand score of competitor company's website is D(60%) this is SS https://prnt.sc/mu1gsz but "wait time" almost none.

So I use wp fastest cache plugin and optimized all photos. I don't think the problem is with my server beacuse i don't experience such a problem on other html websites. i don't understand why this site waiting time is too long?

• I checked your site on GTMetrix https://gtmetrix.com/reports/www.lavidagiyim.com/0ccgExUe and if you see the waterfall result the plugin "yith-woocommerce-wishlist" might be causing high waiting time for each images that it shows. Try testing your site without this plugin.
• You need to also let go of unnecessary plugins as with each added plugin creates a overhead which might leads to high load time.