Hi binzer,
we're told we have to move forward to the 15 m lighting for 125 rvr as its part of the requirements.
As pilots, you are permitted to asses the visual requirements during the first part of the take off roll. (The maths is not that difficult knowing the lights are 30m apart). If you asses you can see adequately then you may continue the take off knowing that the reported RVR further along the runway is satisfactory and that you will have 15m light spacing.
e.g. Consider LGW 08R.
If you lined up at J, the 15m lighting starts 377m along the runway near G.
So having lined up at J, are you seriously expected to taxi over 300m to look at the visual clues adjacent to G?
Otherwise, you may as well taxi the full length of the runway and confirm the mid point and stop end visual requirements are also satisfactory.