Update 3 balance: Halve kiln concrete slab limestone requirements

Currently 18 Limestone + 3 Coal is used to produce 12 concrete bricks using the early Kiln.
The Rotary Kiln once unlocked changes the recipe to 4.5 Limestone 0.75 Coal for the same amount of concrete bricks.
It's clear that the recipe is purposedly inefficient to nudge players into processing slag but it might be a tad bit over the top.
Current recipe only punishes new players who are still learning the ropes and don't know better as experienced players know it's a very early unlock and it should be switched from as soon as possible.
Suggestion:
Halve the Kiln recipe to 9 Limestone 1.5 Coal
This would smooth out the transition and not be as punishing to new players while still provide a big incentive to use the Rotary Kiln.