Yep, new drawing. I keep my eyes open for anything that might be fun to draw up.  This is the second version of this one, I somehow contrived to lose the first vector version. Still can't imagine where I could have put it.

@Dana Ashdown found a photograph of number 15 in her 1887 (final) incarnation, which inspired me to see if I could have a go at producing a reasonable sketch from the photo. As I was going to be colouring the new one I thought I would also colour the previous 1866 rebuild sketch.

1866

Very unusual brake setup for the 1866 rebuild, but I'm confident its a reasonable interpretation of what Ahrons drew in the line drawing I worked this up from.

1887

Looking at the photo carefully I decided it was evident that rather than build a new saddle tank in 1887 Wolverhampton had simply extended the original, which considerably simplified the task. Brakes are more conjectural than I would like, but a similar setup was used by Wolverhampton on early 517s. 
Colour wise, well, its intended to give the impression of Wolverhampton green. Who knows. As ever I've left out the lining and anything else difficult! GWW seems to be silent on the colours of the painted numbers, but white edged in black seemed feasible to me. 

I also added these revised images to the original post after the RMweb site image problems in 2022.

This is interesting! I didn't know you had already done something on this engine.

Although I'm not sure if they are exactly the same, but the Bury's supplied to the London & Birmingham are well documented in Harry Jack's Locomotives of the LNWR Southern Division (The Railway Correspondence & Travel Society, Sawtry, England, 2001). There are some drawings that might be useful.

To my eye the dome over the firebox seems a little too low, relative to the boiler barrel, but thats how it is in the picture, so I wonder how much of the boiler shell was original.

23 hours ago, Dana Ashdown said:

To my eye the dome over the firebox seems a little too low, relative to the boiler barrel, but thats how it is in the picture, so I wonder how much of the boiler shell was original.

According to RCTS no 15 received new boiler barrels in both the 1866 and 1887 rebuilds, but kept the original domed firebox for her entire life. Apparently new frames were fitted in 1890, which seems a surprising repair on such an oddball locomotive. I did have trouble getting a dome shape that I was happy with. 

This document turned up on Facebook...

Presumably Wheatsheaf was a precursor to Croes Newdd Shed? There's nothing about it in my Lyons books on a quick glance, but I see mention of Wheatsheaf junction on line which was very close to Croes Newdd.