I'm going to be cautious and still say old. However the first image has the serial number exposed, just in the shadow so if someone can work some image enhancing magic we might get our answer.
So after lightening and sharping the part of the image w/ the serial number with Pixlr I get the following images.
While the resolution of the images is too low to properly make out all the digits clearly I'm fairly confident that this looks like a 0X2Y serial. The X could be a 1,4 with medium confidence. The Y is the most blurry so I don't want to speculate but it the digits character doesn't appear to be slim.
We know the old J-15 104 had a 0105 serial number and this certainly doesn't look like it. However 104 supposedly suffered heavy damage in 2017 after a bird strike (see post #4,001 by Deino in the J-15 thread). So we have two options, either this is a replacement which I'd expect to be from the earlier batches or a new one from the latest batch.
We also know that serial number 81 was 0408 (=> 104=0431!=0X2Y?) but since we don't exactly know why the J-15 serials are ordered the way they are and because we can't predict the gaps in serials as seen between the 2X, 3X and 6X numbers respectively this can't be viewed as proof against this hypothesis.
There certainly isn't conclusive evidence for either case but on the other hand I see nothing that would make me think that this isn't simply a replacement for 104 from late batch 01.
Also to add I couldn't find the batch number for the new 04 (renumbered 104) to compare.
