Hi, there are no timing signals in the colour signals, that's what the sync pulse is for. The monitor is synchronised to the computer and the computer just spits out the values through the rgb pins at the right time.. The monitor's cannons then draw the equivalent of these pulses in the correct place according to the hsync / vsync.
However, like the two above lha packages' contents tell you, a 15kHz line takes double the amount of time to draw than a 31kHz line. What do you think happens on the screen when you're syncing the monitor to draw two lines in the time that machine uses for sending one?
You need some way to make the colour signal go faster, and I think the only way to do that is to buffer it and then immediately read it twice..