I recommend testing your website using a completely free tool like https://webpagetest.org but be prepared to be shocked especially on mobile performance (make sure you select the appropriate location and device on webpagetest).
Wix has become bloatware and as a result is slow and unresponsive (pun intended). They lack the infrastructure to support the huge number of websites they host, and this means that performance suffers and you can see this in the blocking time and time to first byte.
I have successfully managed to implement CloudFlare (not supported by Wix) which has helped massively with the performance of my site, but the calls to Wix for the content/data which can’t be cached are shockingly slow!
Anyone else having the same issues?