Over supply Breastmilk

I recently gave birth to premature baby and im exclusiveluly pumping for that reason. The Lactation consultant taught me to only pump 15mins for each breast, but I always feel my breast is not yet empty (still feel lumpy). Sometimes its only 2 hrs after pumping, it already painful and lumpy alr. Can I check what mums with oversupply does in this situation? I was told pumping more can simulate more milk but sometimes the pain is unbearable