Well, a level 15 player wouldn't be able to do it full stop (only boss they would be able to fight is Denn the Orcatoothed... unless mini-bosses who don't run away will be included as well) :P

How about this, if someone is level 26, then the "Low Level Boss Rush" will only go to Toto-raks boss fights... or it comes in three different flavours. Easy, Normal and Hard. Easy going up to Toto-rak. Normal going up to Cutter's Cry and then Hard ending at Aurum Vale.