It is possible for more than one IV+level configuration to be optimal for a given Pokémon in a given League. These Pokémon each have a configuration functionally equivalent to their optimal Great League configuration. Note that it might not be generally possible to catch these particular configurations (Legendaries etc. are not typically available below Level 15).
TPokémonOptimumFunctional optima
poisonEkans15-15-15 50 (1048)15-15-14 50 (1044)
electricPikachu15-15-15 50 (1060)15-15-14 50 (1056)
electricFlying Pikachu15-15-15 50 (1060)15-15-14 50 (1056)
electricRock Star Pikachu15-15-15 50 (1060)15-15-14 50 (1056)
electricPop Star Pikachu15-15-15 50 (1060)15-15-14 50 (1056)
electricCaptain Pikachu15-15-15 50 (1060)15-15-14 50 (1056)
electricPikachu Libre15-15-15 50 (1060)15-15-14 50 (1056)
poisonNidoran♂15-15-15 50 (973)15-15-14 50 (969)
grass poisonVileplume0-15-15 22 (1497)0-15-14 22 (1493)
bug grassParas15-15-15 50 (1150)15-15-14 50 (1146)
bug poisonVenonat15-15-15 50 (1135)15-15-14 50 (1132)
groundDiglett15-15-15 50 (764)15-15-14 50 (759)
ground steelAlolan Diglett15-15-15 50 (770)15-15-14 50 (765)
fightingPrimeape1-15-15 24.5 (1500)1-15-14 24.5 (1496)
fire rockHisuian Growlithe15-15-15 50 (1495)15-15-14 50 (1490)
fightingMachoke0-15-15 28 (1498)0-15-14 28 (1494)
water poisonTentacruel1-15-15 23.5 (1500)1-15-14 23.5 (1497)
normal flyingDoduo15-15-15 50 (1357)15-15-14 50 (1352)
poisonMuk0-15-15 20.5 (1496)0-15-14 20.5 (1493)
poison darkAlolan Muk0-15-15 20.5 (1496)0-15-14 20.5 (1493)
rock groundOnix15-15-15 50 (1245)15-15-14 50 (1240)
psychicDrowzee15-15-15 50 (1176)15-15-14 50 (1173)
grass psychicExeggcute15-15-15 50 (1328)15-15-14 50 (1325)
psychic flyingGalarian Articuno0-15-15 15.5 (1500)0-15-14 15.5 (1496)
fire flyingMoltres1-15-15 16 (1500)1-15-14 16 (1497)
grassBayleef3-15-15 50 (1500)3-15-14 50 (1496)
normalSentret15-15-15 50 (698)15-15-14 50 (696)
normal flyingHoothoot15-15-15 50 (766)15-15-14 50 (763)
fairyTogepi15-15-15 50 (743)15-15-14 50 (740)
grass flyingHoppip15-15-15 50 (678)15-15-14 50 (675)
grassSunflora0-15-15 26.5 (1500)0-15-14 26.5 (1496)
darkUmbreon0-15-15 27.5 (1500)0-15-14 27.5 (1497)
fairySnubbull15-15-15 50 (1399)15-15-14 50 (1395)
ghostGalarian Corsola0-15-15 50 (1498)0-15-14 50 (1494)
waterRemoraid15-15-15 50 (1031)15-15-14 50 (1027)
water flyingMantine0-15-14 27.5 (1500)0-15-13 27.5 (1495)
steel flyingSkarmory0-15-14 27.5 (1500)0-15-13 27.5 (1495)
fightingTyrogue15-15-15 50 (556)15-15-14 50 (554)
fire fightingBlaziken1-15-15 19.5 (1499)1-15-14 19.5 (1496)
darkPoochyena15-15-15 50 (766)15-15-14 50 (763)
bug poisonDustox15-15-15 50 (1384)15-15-14 50 (1379)
water grassLombre15-15-15 50 (1353)15-15-14 50 (1349)
grassShroomish15-15-15 50 (916)15-15-14 50 (913)
normalSlakoth15-15-15 50 (1133)15-15-14 50 (1129)
bug groundNincada15-15-15 50 (868)15-15-14 50 (865)
fightingHariyama0-14-14 20 (1500)0-14-13 20 (1497)
fighting psychicMedicham5-15-15 50 (1499)5-15-14 50 (1494)
waterWailord0-15-15 25 (1500)0-15-14 25 (1498)
fire groundNumel15-15-15 50 (1196)15-15-14 50 (1192)
normalSpinda15-15-15 50 (1380)15-15-14 50 (1376)
waterClamperl15-15-15 50 (1436)15-15-14 50 (1430)
waterKyogre0-15-14 13.5 (1500)0-15-13 13.5 (1497)
groundGroudon0-15-14 13.5 (1500)0-15-13 13.5 (1497)
waterPiplup15-15-15 50 (1215)15-15-14 50 (1211)
bug grassWormadam Plant0-15-15 35.5 (1500)0-15-14 35.5 (1495)
bug groundWormadam Sandy0-15-15 35.5 (1500)0-15-14 35.5 (1495)
electricPachirisu15-15-15 50 (1372)15-15-14 50 (1368)
waterFloatzel0-15-14 23 (1500)0-15-13 23 (1496)
dragon groundGarchomp0-15-15 14 (1498)0-15-14 14 (1495)
grass iceSnover15-15-15 50 (1311)15-15-14 50 (1307)
grassTangrowth1-15-15 18.5 (1500)1-15-14 18.5 (1497)
grassServine4-15-15 50 (1499)4-15-14 50 (1494)
water darkHisuian Samurott0-15-15 20 (1498)0-15-14 20 (1494)
ground steelExcadrill2-15-15 17 (1499)2-15-14 17 (1496)
fightingConkeldurr3-15-15 16.5 (1500)3-15-14 16.5 (1497)
psychic flyingSigilyph1-15-15 22 (1500)1-15-14 22 (1496)
rock flyingArchen0-15-15 31 (1500)0-15-14 31 (1495)
normal ghostHisuian Zorua15-15-15 50 (1360)15-15-14 50 (1354)
psychicReuniclus2-15-15 19 (1498)2-15-14 19 (1495)
iceVanilluxe0-15-13 20 (1500)0-15-12 20 (1496)
normal grassDeerling15-15-15 50 (1283)15-15-14 50 (1279)
steelKlang0-15-15 32.5 (1499)0-15-14 32.5 (1495)
electricTynamo15-15-15 50 (917)15-15-14 50 (913)
fightingMienshao0-15-15 20.5 (1500)0-15-14 20.5 (1496)
psychic flyingHisuian Braviary0-15-14 20 (1499)0-15-13 20 (1496)
fireHeatmor0-15-15 23.5 (1498)0-15-14 23.5 (1494)
bug steelDurant1-15-15 21 (1499)1-15-14 21 (1495)
rock fightingTerrakion0-15-15 15 (1498)0-15-14 15 (1495)
dragon iceKyurem1-15-15 15.5 (1498)1-15-14 15.5 (1495)
water fightingKeldeo0-15-15 15 (1498)0-15-14 15 (1495)
water fightingKeldeo Resolute0-15-15 15 (1498)0-15-14 15 (1495)
normal psychicMeloetta Aria0-15-15 14 (1499)0-15-14 14 (1496)
grassChespin15-15-15 50 (1239)15-15-14 50 (1235)
fireBraixen0-15-15 33 (1500)0-15-14 33 (1495)
fire flyingTalonflame0-13-15 26 (1500)0-13-14 26 (1496)
fairySpritzee15-15-15 50 (1415)15-15-14 50 (1412)
dark psychicInkay15-15-15 50 (1048)15-15-14 50 (1045)
rock waterBinacle15-15-15 50 (1069)15-15-14 50 (1065)
normal flyingPikipek15-15-15 50 (1029)15-15-14 50 (1025)
normalGumshoos0-15-13 26 (1500)0-15-12 26 (1496)
bug fairyRibombee1-15-15 25.5 (1498)1-15-14 25.5 (1493)
groundMudsdale0-14-15 18.5 (1500)0-14-14 18.5 (1497)
grassBounsweet15-15-15 50 (532)15-15-14 50 (530)
psychic steelNecrozma Dusk Mane0-15-15 13.5 (1500)0-15-14 13.5 (1496)
psychic ghostNecrozma Dawn Wings0-15-15 13.5 (1500)0-15-14 13.5 (1496)
steelMeltan15-15-15 50 (1207)15-15-14 50 (1203)
fireCinderace0-15-15 18.5 (1500)0-15-14 18.5 (1497)
normalWooloo15-15-15 50 (798)15-15-14 50 (795)
rock fireCarkol0-13-14 50 (1499)0-14-13 50 (1499)
psychicHatenna15-15-15 50 (974)15-15-14 50 (970)
ground normalUrsaluna0-14-15 14.5 (1500)0-14-14 14.5 (1497)
fireFuecoco15-15-15 50 (1274)15-15-14 50 (1271)
fire ghostSkeledirge1-15-15 18.5 (1499)1-15-14 18.5 (1496)
bugTarountula15-15-15 50 (646)15-15-14 50 (643)
electric fightingPawmo15-15-15 50 (1468)15-15-14 50 (1464)
rockNaclstack15-15-15 50 (1461)15-15-14 50 (1457)
darkMaschiff7-15-15 50 (1500)7-15-14 50 (1496)
grass groundToedscruel1-15-15 23.5 (1500)1-15-14 23.5 (1497)
waterWiglett15-15-15 50 (648)15-15-14 50 (645)
rock poisonGlimmora0-15-15 17 (1498)0-15-14 17 (1494)
fighting ghostAnnihilape2-15-15 17 (1499)2-15-14 17 (1497)
Pokémon GO: A Quantitative Approach