Trade speed boosts didn't affect trades with Gold Exchange.
When we discussed the respective bug report in the German forum, I had checked the trade speed to and from the gold exchange on zz2 and zz13. The trade speed was 30 minutes on both worlds (both with trade speed 2), although I had the captain active on zz13, but not active on zz2 at that time.
It was confirmed that the formula for trade movements to and from the gold exchange is 60 minutes (base value) / trade speed of the world (for zz2 and zz13 therefore 60 minutes/2 = 30 minutes), and that neither the captain´s trade speed boost nor event trade speed boosts did affect the actual gold exchange trade speed. It was also confirmed that this behaviour was not intended, i.e. a bug.
Since after today´s update the trade speed is still 30 minutes with the captain´s trade speed boost active, I would guess that either the issue has not yet been fixed or the captain´s speed boost has been excluded for some reason.