There are two things here that seem to be the problem:
First is that the ObjectStyle has a enableTextFrameGeneralOptions
property that needs to be enabled in order for the inset to kick in.
Second is that because you are applying a paragraph style with the same spacing as the object style, you will have double the spacing. So, you should probably remove the paragraph style or turn off it's margin spacing.
// close all your unsaved documents before you run this script
for (var i = 0; i < app.documents.length; i++) {
app.documents[i].close(SaveOptions.NO);
}
var myDocument = app.documents.add(true);
var currentPage = myDocument.spreads.lastItem().pages.lastItem();
myDocument.viewPreferences.horizontalMeasurementUnits = MeasurementUnits.MILLIMETERS;
myDocument.viewPreferences.verticalMeasurementUnits = MeasurementUnits.MILLIMETERS;
myColorWHITE = myDocument.colors.add({name:"WHITE",model:ColorModel.process,colorValue:[0,0,0,0]});
var objectStyleBox = myDocument.objectStyles.add({name:"Box"});
with (objectStyleBox) {
fillTransparencySettings.blendingSettings.opacity = 80;
fillColor = myColorWHITE;
textFramePreferences.insetSpacing = ["15mm","15mm","15mm","15mm"];
enableTextFrameGeneralOptions = true; // Enables general options and inset spacing
autoFit = true;
}
var myObject = currentPage.textFrames.add();
myObject.applyObjectStyle(objectStyleBox);
myObject.geometricBounds = ["25mm","25mm","50mm","120mm"];
myObject.contents = "Milicae is. Ortemnem mium host poteatius lis. At perentilinc tum non diem et quons interet; nonfex milicta demque num. Eci publiae tes re porestem que movena, nos culessi etilissidiem utem. Publis. Fultorum mo vid con verdientime cervivis cri, sena, publictam quit, ur, quemena tamquist grac ret; habena, siderfe conlocr evitio adhui cortuidemeis consum andam aciam ma, fuis ore aucterei ius manum pubis. Fuliceristam octu vignonsulium cum sent, us C. Mus entebatque et videt; horeo, conem avoltor enatus. Scierox mus ommovero, quam inatropotius occi prae et; nos ad me prore cotam teribut audeatquam in demus, abus bonsidem cus sentem dum mo et qua publis? Forit intum inu vis, etem mei senatilis iam eoribut octum idi, sendam aus elut viventeat. Opiorbissi inatur aci fautem ommorac tatuus crem ia? Hosulium perbemurbit."
+ "Il tatum abem sulius pubis perfir la re ius vivir unirmis, popos, oribuntim hocchi, quam veresultuam invo, que facien hocciendet videt? Ficae ad pror quem iam nu virid imus abus num nihil hocupplintem acchicivis, senditua quam etore queremur aderibus iaet? Ximodit rudemus addum nononsus et; horementi, se con Etra, que atum ta, se teniris essoltustia erum tem fuem defatus clem peris horicaedeesi ina, utum facientem atu quodiora te in Itam qua re me ori, nes conihi, supplica publicae conc or aurbist abefex satam es nihi, pratienatum auciste beffren deriti serrionficia et vigit quitiac turnihil vidium foraequam in pori peciviu es! Ximus bonveraes imoena, mus niquid popubis ad nonsu modius, cus iam con in tea occidici ipieris ulicute nonclud emuressi ina, crem, neris,";
myObject.fit(FitOptions.FRAME_TO_CONTENT);