What would you improve?

Bounce rate is quite an unusual metric. It is widely considered that a high bounce rate is bad, but it’s not always that simple and something that has been discussed before. Having said that, I think 40% is quite respectable and would not consider it an issue at that.

If speed is causing bounce, then it’s not good (if you are sure speed is the issue).
According to Pingdom your page size is 1.2MB which is not too far out of the way by modern standards.
It shows that largest part of the site (94.2% of it) is not images, but script. That is something I have noticed with Wix sites, that they are totally reliant on javascript to display anything at all. I don’t want to fire up the whole argument of “relevance of progressive enhancement in 2017” here, but it grates a bit how it’s just a blank page, without even the minimum token effort of a noscript message telling you js must be enabled.