Not only is it possible to reduce the speed of light, but it is impossible to measure the speed of light unless it has been reduced because light moving though a medium other than space will not be traveling at C - but will be traveling slower because of interference with matter (not necessarily molecules).
However your particular question might be rooted in the fact that light will always be measured as moving at V (reduced speed of light) no matter the velocity of the observer -- even if the observer is moving at .9V. So in a sense light cannot be measured at moving slower that V in any given medium -- but that velocity is most likely not as fast as C.
There are equations for calculating the speed of light in different mediums (such as air).
V=C/N where N is the refractive index of the medium. So, in air (which has a refractive index very close to 1), light is nearly moving at 3.00x10^8 m/s. However, in water (which has a refractive index of 1.33) the speed of light would be closer to 2.25x10^8 m/s.
There is a famous experiment where physicists measured the speed of light in Bose-Einstein condensate. Light travels at 38 MPH in Bose-Einstein condensate, slower than a vehicle on the freeway.
But I have read in Special Theory of relativity that we CAN make light take more time to travel a distance.
However, as far as a photon is concerned it does not experience time. A photon can travel anywhere in the universe in an instant. I recommend you look at the relativistic velocity equations. You should find, if you solve the equation for time, with velocity=c, that the time will be undefined.
The trick with relativity is understanding that 1-you will never be able to understand it completely, and 2-the frame of reference can make all the difference, understanding a problem and all the frames involved can be the hardest part of solving it.