diff --git a/lib/types/documentArray/methods/index.js b/lib/types/documentArray/methods/index.js
index dae1baf105..8f918f6a32 100644
--- a/lib/types/documentArray/methods/index.js
+++ b/lib/types/documentArray/methods/index.js
@@ -2,7 +2,6 @@
 
 const ArrayMethods = require('../../array/methods');
 const Document = require('../../../document');
-const castObjectId = require('../../../cast/objectid');
 const getDiscriminatorByValue = require('../../../helpers/discriminator/getDiscriminatorByValue');
 const internalToObjectOptions = require('../../../options').internalToObjectOptions;
 const utils = require('../../../utils');
@@ -121,23 +120,34 @@ const methods = {
    *
    * @return {EmbeddedDocument|null} the subdocument or null if not found.
    * @param {ObjectId|String|Number|Buffer} id
-   * @TODO cast to the _id based on schema for proper comparison
    * @method id
    * @api public
    * @memberOf MongooseDocumentArray
    */
 
   id(id) {
-    let casted;
-    let sid;
-    let _id;
+    if (id == null) {
+      return null;
+    }
+
+    const schemaType = this[arraySchemaSymbol];
+    let idSchemaType = null;
+
+    if (schemaType && schemaType.schema) {
+      idSchemaType = schemaType.schema.path('_id');
+    } else if (schemaType && schemaType.casterConstructor && schemaType.casterConstructor.schema) {
+      idSchemaType = schemaType.casterConstructor.schema.path('_id');
+    }
 
-    try {
-      casted = castObjectId(id).toString();
-    } catch (e) {
-      casted = null;
+    let castedId = null;
+    if (idSchemaType) {
+      try {
+        castedId = idSchemaType.cast(id);
+      } catch (_err) {}
     }
 
+    let _id;
+
     for (const val of this) {
       if (!val) {
         continue;
@@ -145,18 +155,20 @@ const methods = {
 
       _id = val.get('_id');
 
-      if (_id === null || typeof _id === 'undefined') {
+      if (_id == null) {
         continue;
       } else if (_id instanceof Document) {
-        sid || (sid = String(id));
-        if (sid == _id._id) {
+        _id = _id.get('_id');
+        if (castedId != null && utils.deepEqual(castedId, _id)) {
           return val;
-        }
-      } else if (!isBsonType(id, 'ObjectId') && !isBsonType(_id, 'ObjectId')) {
-        if (id == _id || utils.deepEqual(id, _id)) {
+        } else if (castedId == null && (id == _id || utils.deepEqual(id, _id))) {
+          // Backwards compat: compare user-specified param to _id using loose equality
           return val;
         }
-      } else if (casted == _id) {
+      } else if (castedId != null && utils.deepEqual(castedId, _id)) {
+        return val;
+      } else if (castedId == null && (_id == id || utils.deepEqual(id, _id))) {
+        // Backwards compat: compare user-specified param to _id using loose equality
         return val;
       }
     }
diff --git a/test/types.documentarray.test.js b/test/types.documentarray.test.js
index 2acae98f08..8137f33648 100644
--- a/test/types.documentarray.test.js
+++ b/test/types.documentarray.test.js
@@ -83,7 +83,7 @@ describe('types.documentarray', function() {
     sub1.title = 'Hello again to all my friends';
     let id = sub1.id;
 
-    let a = new MongooseDocumentArray([sub1]);
+    let a = new MongooseDocumentArray([sub1], 'test', null);
     assert.equal(a.id(id).title, 'Hello again to all my friends');
     assert.equal(a.id(sub1._id).title, 'Hello again to all my friends');
 
@@ -186,8 +186,23 @@ describe('types.documentarray', function() {
 
     a = new MongooseDocumentArray([sub]);
     assert.equal(a.id(id).title, 'Hello again to all my friends');
+  });
+
+  it('#id with custom schematype (gh-15725)', function() {
+    const schema = new Schema({ _id: Number, name: String });
+    const Subdocument = TestDoc(schema);
+
+    const sub1 = new Subdocument();
+    sub1._id = 42;
+    sub1.title = 'Hello again to all my friends';
 
+    const parentDoc = { $__: true, $__schema: new Schema({ subdocs: [schema] }) };
 
+    const a = new MongooseDocumentArray([sub1], 'subdocs', parentDoc);
+    assert.equal(a.id('42').title, 'Hello again to all my friends');
+    assert.equal(a.id(sub1.id).title, 'Hello again to all my friends');
+    assert.ok(!a.id('43'));
+    assert.ok(!a.id('not a number'));
   });
 
   describe('inspect', function() {