For now it is what it is. You can try to compare the performance of editor link Vs code for opening the lighbox. Maybe one of them will be faster in your case.
I hope Wix will improve the lightbox performance soon.
I too was very excited when prefetchPageResources API came out. However once implemented there was no noticeable change to speed on the website I was working on. Still takes 3-4 seconds for the lightbox to populate.