But can't content of TAsphyreCanvas be copied to regular canvas?

Even if you'd do this pixel-by-pixel (getting pixel's x/y and putting this pixel into normal canvas at proper positions) it shouldn't take long. Unless there is some blitting function to copy from AsphyreCanvas into regular one and vice versa - then it is even faster.

Anyway, JPG is terrible for screenshots as I said earlier and I strongly recommend trying other means to save it at least to bmp (you can then open this bmp with invisible TImage, save as png and remove bmp file to save space).