Mammoth Uncensored Word List:
32 words ending with ls, 15 letters long

biogeochemicals brachydiagonals centibecquerels circumstantials constitutionals counterfactuals dehydroretinols duononagesimals duosexagesimals femtobecquerels hectobecquerels hexatrigesimals megasporophylls microbecquerels millibecquerels nonterrestrials pharmaceuticals psychochemicals quincentennials semicentennials sphaerocrystals subterrestrials tetravigesimals transcendentals trinitrocresols trinitrophenols trinitrotoluols unprofessionals yoctobecquerels yottabecquerels zeptobecquerels zettabecquerels