My two cents here .. reflection maps of course would be quicker.. you could build one from a spherical render of the scene.. but also imho , maybe the 'cast shadows' and/or 'receive shadows'for the glass mat could be unchecked depending on how far away the point of view is from the glass panels. (shadows are great render-time eaters.) -'show caustics' surely can be unchecked too if you put some refraction. but maybe refraction could be avoided too ? no blurred transparency is evident.. these are just some ideas :) good luck ! Paul