Sarge

Michelle, since your wanting to change them from the original exposure time, I would just do both of the at 15 min. but make sure you have a lamp that will perform well in a 15 min session. The ESP or the ESP/R should do the trick. Look at it this way, you will get (4) sessions per hour (lamp hour) vrs. (3) and in the long run you will make more $ per bed. Lamp cost will be the same wether its a 15 min or 20 min session. You will save on electricity per session as well. Good Luck......