I wouldn't worry too much, while they are easy to make, and look 'ok', they actually don't work properly in RW. They display incorrectly on the map, and often the AI dispatcher will mess up and reset the slip as you're travelling over it, resulting in you derailing.
So no, trainz isn't lagging too badly in this regard - double slips may be a pain to place, and look a bit iffy without using fixed-track slips instead of the auto-junctions, but they do at least work, and rarely derail a player.