There are 391 fifteen-letter words containing A, M, S and 2T, https://www.bestwordlist.com/c/a/5/15letterwordswithamstt.htm
ABSORPTIOMETERS ABSTRACTIONISMS ACCLIMATISATION ACHROMATICITIES
ACHROMATISATION ACTINOCHEMISTRY ADMINISTRATIONS AFTERTREATMENTS
AMBIDEXTERITIES ANTHROPOMETRIES ANTHROPOMETRIST ANTHROPOPATHISM
ANTIARRHYTHMICS ANTICAPITALISMS ANTIHELMINTHICS ANTIHISTAMINICS
ANTIMATERIALISM ANTIMATERIALIST ANTIMETABOLITES ANTIMILITARISMS
ANTIMILITARISTS ANTIMONARCHISTS ANTIMONOPOLISTS ANTIRATIONALISM
ANTIROMANTICISM ANTISENTIMENTAL ANTITHROMBOTICS APOPHTHEGMATISE
APOPHTHEGMATIST APOTHEGMATISING APPRENTICEMENTS ARCHAEOMETRISTS
AROMATHERAPISTS ASSIMILATIONIST ASTRODYNAMICIST AUTODIDACTICISM
AUTOMATISATIONS AUTOMATIZATIONS AUTOTRANSFORMER AXIOMATISATIONS
AXIOMATIZATIONS BIOCONTAINMENTS BIOSYSTEMATISTS BITUMINISATIONS
BITUMINIZATIONS CASTRAMETATIONS CENTRIPETALISMS CHEMOAUTOTROPHS
CHEMOTAXONOMIST CHEMOTHERAPISTS CHRESTOMATHICAL CHROMATOLOGISTS
CIRCUMNUTATIONS CIRCUMSTANTIALS CIRCUMSTANTIATE COMMUTABILITIES
COMMUTATIVITIES COMPATIBILITIES COMPOTATIONSHIP COMPUTABILITIES
COMPUTERISATION CONTEMPERATIONS CONTEMPERATURES CONTINENTALISMS
CYTOTAXONOMISTS DECONTAMINATORS DELEGITIMATIONS DEMAGNETISATION
DEMOCRATISATION DEMONETISATIONS DEMONETIZATIONS DEMONSTRABILITY
DEMONSTRATIONAL DEMONSTRATIVELY DEMUTUALISATION DEMYSTIFICATION
DEPARTMENTALISE DEPARTMENTALISM DEPIGMENTATIONS DERMATOMYOSITIS
DERMATOPHYTOSES DERMATOPHYTOSIS DERMATOPLASTIES DETERMINATENESS
DIAPHOTOTROPISM DIAPHRAGMATITIS DICHOTOMISATION DIFFRACTOMETERS
DISAFFORESTMENT DISAPPOINTMENTS DISENCHANTMENTS DISENTANGLEMENT
DISENTHRALLMENT DISENTHRALMENTS DISENTRAINMENTS DISENTRANCEMENT
DISFEATUREMENTS DISHEARTENMENTS DISINTERMEDIATE DISTEMPERATURES
DOLOMITISATIONS DOLOMITIZATIONS ELECTROMOTANCES EMANCIPATIONIST
EPITHELIOMATOUS EXISTENTIALISMS EXPERIMENTALIST EXTEMPORISATION
FUNDAMENTALISTS FUTILITARIANISM GEOMETRISATIONS GEOMETRIZATIONS
GNATHOSTOMATOUS GOVERNMENTALIST GRAMMATICASTERS GRAMMATOLOGISTS
HAEMACYTOMETERS HAEMOCYTOMETERS HEADMASTERLIEST HEMAGGLUTINATES
HETEROTHALLISMS HIEROGRAMMATIST HISTOCOMPATIBLE HOMOTRANSPLANTS
HUMANITARIANIST HYPERSTIMULATED HYPERSTIMULATES HYPOPITUITARISM
ILLEGITIMATIONS IMITATIVENESSES IMMATERIALITIES IMMORTALISATION
IMMUNOSTIMULANT IMPARTIBILITIES IMPERTURBATIONS IMPLEMENTATIONS
IMPORTABILITIES IMPORTUNATENESS IMPOSTHUMATIONS INCREMENTALISTS
INFORMATISATION INIMITABILITIES INSTRUMENTALISM INSTRUMENTALIST
INSTRUMENTALITY INSTRUMENTATION INTELLECTUALISM INTEMPERATENESS
INTERACTIONISMS INTERANIMATIONS INTERMEDIATIONS INTERMIGRATIONS
INTERVALOMETERS INTERWEAVEMENTS INTRANSIGENTISM INTUITIONALISMS
LAMELLIROSTRATE LEGITIMISATIONS LEGITIMIZATIONS LIPOGRAMMATISTS
LITHOCHROMATICS MACROSTRUCTURAL MACROSTRUCTURES MAGISTRATESHIPS
MAGISTRATICALLY MALDISTRIBUTION MALPRESENTATION MANIFESTATIONAL
MARKETABILITIES MARTENSITICALLY MASSOTHERAPISTS MASTOIDECTOMIES
MATERIALISATION MATERIALISTICAL MATHEMATICISING MATHEMATISATION
MATRIFOCALITIES MATRILOCALITIES MEGAVERTEBRATES MENTALISTICALLY
METABISULPHITES METACHROMATISMS METAFICTIONISTS METALINGUISTICS
METALLOGRAPHIST METAMATHEMATICS METAMICTISATION METASTABILITIES
METHYLXANTHINES METROPOLITANISE METROPOLITANISM MICROPEGMATITES
MICROSATELLITES MICROSTRUCTURAL MICROTONALITIES MILITARISATIONS
MILITARIZATIONS MINIATURISATION MINISTERIALISTS MISACCEPTATIONS
MISARTICULATING MISARTICULATION MISATTRIBUTIONS MISCOMPUTATIONS
MISORIENTATIONS MISPUNCTUATIONS MISREGISTRATION MISTRANSLATIONS
MISUTILISATIONS MISUTILIZATIONS MONOUNSATURATED MONOUNSATURATES
MONUMENTALITIES MULTICANDIDATES MULTICHARACTERS MULTILATERALISM
MULTILATERALIST MULTIPARAMETERS MULTIPLICATIONS MULTIPOLARITIES
MULTITHREADINGS MYLONITISATIONS MYLONITIZATIONS MYTHOLOGISATION
NEUROANATOMISTS NEUROBLASTOMATA NOCTAMBULATIONS NONIMPORTATIONS
NONINSTALLMENTS NONINSTRUMENTAL NUMISMATOLOGIST ODONTOSTOMATOUS
OPHTHALMOLOGIST OPHTHALMOMETERS OPISTHOGNATHISM OPTIMALISATIONS
OPTIMALIZATIONS ORTHOCHROMATISM OVERADJUSTMENTS OVERESTIMATIONS
OVERSTIMULATING OVERSTIMULATION PALAEOMAGNETIST PALEOMAGNETISTS
PANOPHTHALMITIS PANTOPRAGMATICS PARAGRAMMATISTS PARAMETRISATION
PARASYMPATHETIC PENTADACTYLISMS PERIPATETICISMS PERMUTABILITIES
PHANTASMALITIES PLAGIOSTOMATOUS PNEUMATOLOGISTS PNEUMATOMETRIES
POSTMASTERSHIPS POSTSTIMULATION POSTSTIMULATORY PRAGMATISATIONS
PRAGMATIZATIONS PREFORMATIONIST PRESENTATIONISM PRETERMINATIONS
PROMOTABILITIES PROSTATECTOMIES PSEUDOMUTUALITY QUARTERMISTRESS
QUATTROCENTISMS RADIOSTRONTIUMS RADIOTELEMETERS READVERTISEMENT
REESTABLISHMENT REFORMATIONISTS REFRACTOMETRIES REIMPLANTATIONS
REMONETISATIONS REMONETIZATIONS REMONSTRATINGLY REMONSTRATIVELY
RESTORATIONISMS RESYSTEMATISING RESYSTEMATIZING RETINOBLASTOMAS
RHEUMATOLOGISTS ROMANTICALITIES ROMANTICISATION SACRAMENTALISTS
SCHEMATISATIONS SCHEMATIZATIONS SEMIABSTRACTION SEMITERRESTRIAL
SEMITRANSLUCENT SEMITRANSPARENT SENTIMENTALISED SENTIMENTALISES
SENTIMENTALISMS SENTIMENTALISTS SENTIMENTALIZED SENTIMENTALIZES
SIMPLICIDENTATE SPERMATOBLASTIC SPERMATOGENETIC STALAGMITICALLY
STALAGMOMETRIES STIGMATISATIONS STIGMATIZATIONS STIGMATOPHILIAS
STIGMATOPHILIST STOMATOPLASTIES STRABISMOMETERS SUBMETACENTRICS
SUBOPTIMISATION SUBOPTIMIZATION SUBSTANTIALISMS SUPERPATRIOTISM
SUPERSTIMULATED SUPERSTIMULATES SUPPLEMENTATION SYMMETRISATIONS
SYMMETRIZATIONS SYMPATHECTOMIES SYMPATHETICALLY SYMPATHOMIMETIC
SYMPTOMATICALLY SYMPTOMATOLOGIC SYSTEMATISATION SYSTEMATIZATION
SYSTEMATOLOGIES TARSOMETATARSAL TARSOMETATARSUS TATTERDEMALIONS
TELOMERISATIONS TELOMERIZATIONS TEMPERABILITIES TEMPERATENESSES
TEMPTABLENESSES TERMINABILITIES TERRITORIALISMS TESTIMONIALISED
TESTIMONIALISES TESTIMONIALIZED TESTIMONIALIZES TETARTOHEDRISMS
TETRAGRAMMATONS TETRASPORANGIUM THAUMATOLATRIES THERIANTHROPISM
THERMAESTHESIAS THERMALISATIONS THERMALIZATIONS THERMOREGULATES
THERMOSTABILITY THERMOTHERAPIES THREMMATOLOGIES THROMBOPLASTINS
TOASTMISTRESSES TOTALITARIANISM TRADITIONALISMS TRANSAMINATIONS
TRANSFIGUREMENT TRANSFORMATIONS TRANSILLUMINATE TRANSMIGRATIONS
TRANSMISSOMETER TRANSMITTANCIES TRANSMUTABILITY TRANSMUTATIONAL
TRANSVESTITISMS TRAUMATISATIONS TRAUMATIZATIONS TRAUMATONASTIES
TRIHALOMETHANES TRIIODOMETHANES TRIMETHYLAMINES TYNDALLIMETRIES
ULTRAMICROTOMES ULTRAMODERNISTS ULTRAMONTANISMS ULTRAMONTANISTS
UNDEMONSTRATIVE UNDERESTIMATING UNDERESTIMATION UNDERSTATEMENTS
UNDOMESTICATING UNMITIGATEDNESS UNSENTIMENTALLY UNSTATESMANLIKE
UNTRANSMIGRATED UTILITARIANISMS VESTIMENTIFERAN