not sure what 14 h do mean without knowing your tech specs, but anyway, a few tips - maybe you already know them...
make sure you didn't use any reflectance 0 value with a single RGB entry at 255 or just below. personally i stay under 230, but in any case, stay under 240, this results in clearing up noise much faster. the reflectance 90 value has no influence on this.
also, try to keep emitters as simple as possible. don't place emitters behind dielectrics if you can avoid it. and, as already suggested, add an invisible emitter plane with the same camera direction, this helps to 'fill' the interior with additional light. be careful not to set this emitter too high, if not you will get the well known 'flash' effect.
cheers
markus