Is it possible to lock one UV island and scale other (same) to be the same size as the locked one? I have tried pinning the big island and Ctrl + A (averaging both of the islands), but that scales both of them down (making them the same size). I want the big one to not change its size and only the small one to scale up to match the big one. I hope it makes sense.
Thanks,
Snapping

Or if they are the same size - by using the Texel Density Checker Addon https://gumroad.com/l/CEIOR