Attempt with Ray Differentials. Render time 10sec
Regular texture mapping. Render time 6sec
As the ray shoots further into the distance the direction becomes almost parallel to the plane so plane bias check has to be adjusted. Otherwise you get sky on your floor
Specs
Processor: Inter(R) Core i7-35337 CPU @ 2.00Ghz
RAM 8.00GB
NVIDIA GeForce GT 740M