There are 415 fifteen-letter words containing A, G, R, S and T, https://www.bestwordlist.com/c/a/5/15letterwordswithagrst.htm
ABORIGINALITIES AEROLITHOLOGIES AGGRANDISEMENTS AGGRANDIZEMENTS
AGGREGATENESSES AGRANULOCYTOSES AGRANULOCYTOSIS AGRICULTURALIST
ALLEGORISATIONS ALLEGORIZATIONS ALLERGENICITIES ANAGRAMMATISING
ANGUSTIROSTRATE ANTHROPOGENESES ANTHROPOGENESIS ANTHROPOLOGISTS
ANTHROPOPHAGIES ANTHROPOPHAGOUS ANTICARCINOGENS ANTIOESTROGENIC
ANTIPROGRESSIVE ANTISEGREGATION APPROXIMEETINGS ARCHEOMAGNETISM
ARCHEOZOOLOGIST ARCHGENETHLIACS ARTERIOGRAPHIES ARTIFICIALISING
ASTROBIOLOGISTS ASTROGEOLOGISTS ASTRONAVIGATION ASTRONAVIGATORS
ASTROPHOTOGRAPH AUTOBIOGRAPHERS AUTOBIOGRAPHIES AUTODESTRUCTING
AUTORADIOGRAPHS BACKSCATTERINGS BACKSCRATCHINGS BACTERIOLOGISTS
BACTERIOPHAGIES BACTERIOPHAGOUS BIODEGRADATIONS BIOREGIONALISTS
BIOSTRATIGRAPHY BLACKGUARDLIEST BREMSSTRAHLUNGS BUREAUCRATISING
CARPETBAGGERIES CATEGORICALNESS CATEGORISATIONS CATEGORIZATIONS
CATHODOGRAPHERS CATHODOGRAPHIES CENTRIFUGALISED CENTRIFUGALISES
CENTRIFUGALIZES CENTRIFUGATIONS CHALCOGRAPHISTS CHARGEABILITIES
CHROMATOLOGISTS CIRCUMGYRATIONS CIRCUMNAVIGATES CLIMATOGRAPHIES
COADMINISTERING COINVESTIGATORS COLLATERALISING COMMISERATINGLY
CONGLOMERATEURS CONGLOMERATIONS CONGRATULATIONS CONNATURALISING
CORINTHIANISING COUNTERSHADINGS COUNTERSTAINING COUNTERSTRATEGY
CREDENTIALLINGS CROSSOPTERYGIAN CRYPTOGRAPHISTS CRYSTALLOGRAPHY
CYBERSQUATTINGS CYTOMEGALOVIRUS DACTYLOGRAPHERS DACTYLOGRAPHIES
DAGUERREOTYPERS DAGUERREOTYPIES DAGUERREOTYPIST DEGENERATIONIST
DEGLAMORISATION DEGRADABILITIES DEMATERIALISING DEREGISTRATIONS
DERMATOGLYPHICS DERMATOGRAPHIAS DERMATOGRAPHIES DIAPHRAGMATITIS
DIAPHRAGMITISES DISAGGREGATIONS DISAGREEABILITY DISARRANGEMENTS
DISARTICULATING DISCOURAGEMENTS DISHEARTENINGLY DISINTEGRATIONS
DISINTHRALLINGS DISINVIGORATING DISNATURALISING DISNATURALIZING
DISORGANISATION DISORGANIZATION DOCUMENTARISING DOWNREGULATIONS
DRAUGHTSMANSHIP DRAUGHTSPERSONS EARTHSHATTERING EGALITARIANISMS
ELECTROGRAPHIES ELECTROMYOGRAMS ELECTROPLATINGS ELECTROSURGICAL
EMPYREUMATISING ENTEROGASTRONES EPIGRAMMATISERS EPIGRAMMATISING
EPIGRAMMATIZERS ESTRANGEDNESSES EVANGELISTARIES EVANGELISTARION
EVERLASTINGNESS EXAGGERATEDNESS EXTRALINGUISTIC FARTHINGSWORTHS
FEATHERBEDDINGS FERRIMAGNETISMS FERROMAGNETISMS FIBROCARTILAGES
FRACTIONALISING FRAGMENTARINESS GALVANOTROPISMS GASTROENTERITIC
GASTROENTERITIS GASTRONOMICALLY GENERALISATIONS GENERALIZATIONS
GENTRIFICATIONS GEOMETRISATIONS GEOMETRIZATIONS GEOSTROPHICALLY
GERMINABILITIES GEWURZTRAMINERS GINGERBREADIEST GLUTARALDEHYDES
GOVERNABILITIES GOVERNMENTALISE GOVERNMENTALISM GOVERNMENTALIST
GRAMMATICALNESS GRAMMATICASTERS GRAMMATOLOGISTS GRANGERISATIONS
GRANGERIZATIONS GRANULITISATION GRAPHITISATIONS GRAPHITIZATIONS
GREISENISATIONS GREISENIZATIONS GUTTURALISATION GYROSTABILISERS
GYROSTABILIZERS HIEROGRAMMATIST HISTORIOGRAPHER HISTORIOGRAPHIC
HYDROGENISATION IATROGENICITIES IMMATERIALISING INDUSTRIALISING
INDUSTRIALIZING INORGANISATIONS INORGANIZATIONS INTEGRABILITIES
INTEGRATIONISTS INTERGRADATIONS INTERMIGRATIONS INTEROSCULATING
INTERROGATORIES INTRANSIGEANCES INTRANSIGEANTLY INTRANSIGENCIES
INTRANSIGENTISM INTRANSIGENTIST IRRATIONALISING KINDERGARTENERS
LARYNGECTOMISED LARYNGOSCOPISTS LEGERDEMAINISTS LEGISLATORSHIPS
LEXICOGRAPHISTS LIPOGRAMMATISMS LIPOGRAMMATISTS MACROAGGREGATES
MACROMARKETINGS MAGISTERIALNESS MAGISTRATESHIPS MAGISTRATICALLY
MARGARITIFEROUS MARGINALISATION MEGAVERTEBRATES MELODRAMATISING
METAGRABOLISING METAGROBOLISING METALLOGRAPHERS METALLOGRAPHIES
METALLOGRAPHIST MICROMARKETINGS MICROPEGMATITES MISAPPRECIATING
MISARRANGEMENTS MISARTICULATING MISREGISTRATION MISTRANSCRIBING
MONGRELISATIONS MONGRELIZATIONS MOUNTAINEERINGS MULTITHREADINGS
NEARSIGHTEDNESS NEUROMARKETINGS NIGHTMARISHNESS NITROGENISATION
NONSEGREGATIONS NOTHINGARIANISM OESTROGENICALLY OLIGOMERISATION
OPISTHOGRAPHIES ORGANOGRAPHISTS ORGANOMETALLICS ORGANOPHOSPHATE
ORGANOTHERAPIES ORTHOGONALISING ORTHOGONALITIES OSMOREGULATIONS
OVERADVERTISING OVERDRAMATISING OVEREXAGGERATES OVERMANAGEMENTS
OVERREGULATIONS OVERSPECULATING OVERSTIMULATING PALAEOGRAPHISTS
PAMPHLETEERINGS PANTOPRAGMATICS PARAGRAMMATISTS PARALINGUISTICS
PARASITOLOGICAL PARASITOLOGISTS PARTHENOGENESES PARTHENOGENESIS
PARTICULARISING PATRONIZINGNESS PEDESTRIANISING PEDESTRIANIZING
PERGAMENTACEOUS PERIGASTRITISES PERINATOLOGISTS PHANTASMAGORIAL
PHANTASMAGORIAS PHANTASMAGORIES PHARMACOGNOSIST PHARMACOGNOSTIC
PHARMACOLOGISTS PHARYNGOLOGISTS PHOSPHORYLATING PHOTOENGRAVINGS
PHOTOTELEGRAPHS PLETHYSMOGRAPHS PLETHYSMOGRAPHY POSTGRADUATIONS
POSTHEMORRHAGIC PRAGMATICALNESS PRAGMATISATIONS PRAGMATIZATIONS
PREARRANGEMENTS PREDESIGNATIONS PREESTABLISHING PRENEGOTIATIONS
PREREGISTRATION PRESTIDIGITATOR PROCRASTINATING PROGNOSTICATING
PROGNOSTICATION PROGNOSTICATIVE PROGNOSTICATORS PROPAGABILITIES
PSYCHOGERIATRIC PTERYLOGRAPHIES PYRAMIDOLOGISTS PYROPHOTOGRAPHS
QUARTERBACKINGS QUINGENTENARIES RADIOAUTOGRAPHS RADIOBIOLOGISTS
RADIOTELEGRAPHS RANGATIRATANGAS REACCLIMATISING READMINISTERING
RECOGNISABILITY RECONSOLIDATING RECRYSTALLISING RECRYSTALLIZING
REDINTEGRATIONS REFRIGERATORIES REGIONALISATION REGULARISATIONS
REGULARIZATIONS REHOSPITALISING REHOSPITALIZING REINVESTIGATING
REINVESTIGATION REINVIGORATIONS REMATERIALISING REMONSTRATINGLY
RENATIONALISING REORCHESTRATING REORGANISATIONS REORGANIZATIONS
REREGISTRATIONS RESYSTEMATISING RESYSTEMATIZING RETROGRADATIONS
RETROGRESSIONAL RHEUMATOLOGISTS RIGHTABLENESSES RIGIDIFICATIONS
ROENTGENISATION ROENTGENOGRAPHS RONTGENISATIONS RONTGENIZATIONS
SACERDOTALISING SACERDOTALIZING SAPROGENICITIES SAUROPTERYGIANS
SCHOOLMASTERING SCRATCHBUILDING SEGREGATIONISTS SELENOGRAPHISTS
SEMILOGARITHMIC SEPTUAGENARIANS SINGULARISATION SINGULARIZATION
SLAUGHTERHOUSES SPECTROGRAPHIES SPERMATOGENESES SPERMATOGENESIS
SPERMATOGENETIC STALAGMOMETRIES STEGANOGRAPHERS STEGANOGRAPHIES
STEGANOGRAPHIST STEREOGRAPHICAL STEREOLOGICALLY STOCKBROKERAGES
STRAIGHTFORWARD STRAIGHTJACKETS STRAITJACKETING STRATIGRAPHICAL
STRATIGRAPHISTS STRIKEBREAKINGS STRUCTURALISING STRUCTURALIZING
SUBAGGREGATIONS SUBCATEGORISING SUBCATEGORIZING SUBCONTRACTINGS
SUBORGANISATION SUBORGANIZATION SUPEREROGATIONS SUPERORDINATING
SUPERORGANICIST SUPERSATURATING SUSPERCOLLATING SYNERGISTICALLY
TELAUTOGRAPHIES TELEPHOTOGRAPHS TERATOGENICISTS TERGIVERSATIONS
TETRAGRAMMATONS TETRASPORANGIUM THALASSOGRAPHER THALASSOGRAPHIC
THANATOGRAPHIES THEATRICALISING THERMOREGULATES THREMMATOLOGIES
TRANQUILISINGLY TRANSFIGURATION TRANSFIGUREMENT TRANSGENDERISMS
TRANSGRESSIONAL TRANSGRESSIVELY TRANSISTORISING TRANSISTORIZING
TRANSLITERATING TRANSMIGRATIONS TRANSMOGRIFYING TRIANGULARITIES
TURBOGENERATORS ULTRASONOGRAPHY UNCATEGORISABLE UNDERESTIMATING
UNDERGRADUETTES UNDERSTANDINGLY UNORIGINALITIES UNTRANSMIGRATED
UPGRADABILITIES UTEROGESTATIONS ZYGOBRANCHIATES