diff --git a/web/ui/module/codemirror-promql/src/complete/hybrid.test.ts b/web/ui/module/codemirror-promql/src/complete/hybrid.test.ts
index 526a5ce4f8..587e9c5304 100644
--- a/web/ui/module/codemirror-promql/src/complete/hybrid.test.ts
+++ b/web/ui/module/codemirror-promql/src/complete/hybrid.test.ts
@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import { analyzeCompletion, computeStartCompletePosition, ContextKind } from './hybrid';
+import { analyzeCompletion, computeStartCompletePosition, ContextKind, durationWithUnitRegexp } from './hybrid';
 import { createEditorState, mockedMetricsTerms, mockPrometheusServer } from '../test/utils-test';
 import { Completion, CompletionContext } from '@codemirror/autocomplete';
 import {
@@ -559,6 +559,18 @@ describe('analyzeCompletion test', () => {
       pos: 28,
       expectedContext: [{ kind: ContextKind.Duration }],
     },
+    {
+      title: 'do not autocomplete duration when unit already present in matrixSelector',
+      expr: 'rate(foo[5m])',
+      pos: 10,
+      expectedContext: [],
+    },
+    {
+      title: 'do not autocomplete duration when multi char unit already present in matrixSelector',
+      expr: 'rate(foo[5ms])',
+      pos: 10,
+      expectedContext: [],
+    },
     {
       title: 'autocomplete duration for a subQuery',
       expr: 'go[5d:5]',
@@ -630,6 +642,42 @@ describe('analyzeCompletion test', () => {
   });
 });
 
+describe('durationWithUnitRegexp test', () => {
+  it('should match complete durations with units', () => {
+    const testCases = [
+      { input: '5m', expected: true },
+      { input: '30s', expected: true },
+      { input: '1h', expected: true },
+      { input: '500ms', expected: true },
+      { input: '2d', expected: true },
+      { input: '1w', expected: true },
+      { input: '1y', expected: true },
+      { input: '1d2h', expected: true },
+      { input: '2h30m', expected: true },
+      { input: '1h2m3s', expected: true },
+      { input: '250ms2s', expected: true },
+      { input: '2h3m4s5ms', expected: true },
+      { input: '5', expected: false },
+      { input: '5m5', expected: false },
+      { input: 'm', expected: false },
+      { input: 'd', expected: false },
+      { input: '', expected: false },
+      { input: '1hms', expected: false },
+      { input: '2x', expected: false },
+    ];
+    testCases.forEach(({ input, expected }) => {
+      expect(durationWithUnitRegexp.test(input)).toBe(expected);
+    });
+  });
+
+  it('should not match durations without units or partial units', () => {
+    const testCases = ['5', '30', '100', '5m5', 'm', 'd'];
+    testCases.forEach((input) => {
+      expect(durationWithUnitRegexp.test(input)).toBe(false);
+    });
+  });
+});
+
 describe('computeStartCompletePosition test', () => {
   const testCases = [
     {
@@ -1229,6 +1277,28 @@ describe('autocomplete promQL test', () => {
         validFor: undefined,
       },
     },
+    {
+      title: 'offline do not autocomplete duration when unit already present in matrixSelector',
+      expr: 'rate(foo[5m])',
+      pos: 10,
+      expectedResult: {
+        options: [],
+        from: 10,
+        to: 10,
+        validFor: /^[a-zA-Z0-9_:]+$/,
+      },
+    },
+    {
+      title: 'offline do not autocomplete duration when multi char unit already present in matrixSelector',
+      expr: 'rate(foo[5ms])',
+      pos: 10,
+      expectedResult: {
+        options: [],
+        from: 10,
+        to: 10,
+        validFor: /^[a-zA-Z0-9_:]+$/,
+      },
+    },
     {
       title: 'offline autocomplete duration for a subQuery',
       expr: 'go[5d:5]',
diff --git a/web/ui/module/codemirror-promql/src/complete/hybrid.ts b/web/ui/module/codemirror-promql/src/complete/hybrid.ts
index 76efc34442..814147e532 100644
--- a/web/ui/module/codemirror-promql/src/complete/hybrid.ts
+++ b/web/ui/module/codemirror-promql/src/complete/hybrid.ts
@@ -166,6 +166,19 @@ function arrayToCompletionResult(data: Completion[], from: number, to: number, i
   } as CompletionResult;
 }
 
+// Matches complete PromQL durations, including compound units (e.g., 5m, 1d2h, 1h30m, etc.).
+// Duration units are a fixed, safe set (no regex metacharacters), so no escaping is needed.
+export const durationWithUnitRegexp = new RegExp(`^(\\d+(${durationTerms.map((term) => term.label).join('|')}))+$`);
+
+// Determines if a duration already has a complete time unit to prevent autocomplete insertion (issue #15452)
+function hasCompleteDurationUnit(state: EditorState, node: SyntaxNode): boolean {
+  if (node.from >= node.to) {
+    return false;
+  }
+  const nodeContent = state.sliceDoc(node.from, node.to);
+  return durationWithUnitRegexp.test(nodeContent);
+}
+
 // computeStartCompleteLabelPositionInLabelMatcherOrInGroupingLabel calculates the start position only when the node is a LabelMatchers or a GroupingLabels
 function computeStartCompleteLabelPositionInLabelMatcherOrInGroupingLabel(node: SyntaxNode, pos: number): number {
   // Here we can have two different situations:
@@ -477,12 +490,18 @@ export function analyzeCompletion(state: EditorState, node: SyntaxNode, pos: num
         //   Duration, Duration, ⚠(NumberLiteral)
         // )
         // So we should continue to autocomplete a duration
-        result.push({ kind: ContextKind.Duration });
+        if (!hasCompleteDurationUnit(state, node)) {
+          result.push({ kind: ContextKind.Duration });
+        }
       } else {
         result.push({ kind: ContextKind.Number });
       }
       break;
     case NumberDurationLiteralInDurationContext:
+      if (!hasCompleteDurationUnit(state, node)) {
+        result.push({ kind: ContextKind.Duration });
+      }
+      break;
     case OffsetExpr:
       result.push({ kind: ContextKind.Duration });
       break;