Śatapatha Brāhmaṇa ("of a hundred paths") 11.1.2.13

11.1.2.13

sa ājisṛtāmekaḥ ya evaṃ vidvāṃstriṃśataṃ varṣāṇi yajate tasmādu triṃśatameva varṣāṇi yajeta yadyu dākṣāyaṇayajñī syādatho api pañcadaśaiva varṣāṇi yajetātra hyeva sā sampatsampadyate dve hi paurṇamāsyau yajate dve amāvāsye atro eva khalu sā sampadbhavati

He who, knowing this, offers (the Full and New-moon sacrifice) for thirty years, becomes one of the race-runners, whence one ought to offer sacrifice for not less than thirty years. But if he be a performer of the Dâkshâyana sacrifice, he need only offer for fifteen years, for therein that perfection is brought about, since he performs (every month) two Full-moon and two New-moon offerings, and thus that perfection is indeed brought about therein.