diff --git a/frontend/src/components/preview/PreviewImage.tsx b/frontend/src/components/preview/PreviewImage.tsx
index 09d070b..6c65232 100644
--- a/frontend/src/components/preview/PreviewImage.tsx
+++ b/frontend/src/components/preview/PreviewImage.tsx
@@ -59,21 +59,30 @@ function PreviewStillImage({ photo }: { photo: Photo }) {
   const fullResSrc = getPreviewFullResSrc(photo)
   const src = usingFullRes ? fullResSrc : thumbSrc
 
-  // Reset everything when the photo changes, then start the background
-  // full-res preload. Cancel the preloader's callback on unmount/change so a
-  // late-arriving onload from the previous photo can't flip state for the
-  // current one.
+  // Reset everything when the photo changes, then queue a *debounced*
+  // background full-res preload. Debouncing matters because `new Image()`
+  // requests can't be aborted: rapid arrow-nav would otherwise leave a
+  // dozen multi-MB /proxy fetches in flight, saturating the user's
+  // bandwidth (and the backend's transcoder for RAW/HEIC) for photos the
+  // user already navigated past. Only photos the user lingers on for
+  // FULL_RES_PRELOAD_DELAY_MS trigger the /proxy fetch.
   useEffect(() => {
     setLoaded(false)
     setUsingFullRes(false)
     setScale(1)
     setOffset({ x: 0, y: 0 })
 
-    const preloader = new Image()
-    preloader.onload = () => setUsingFullRes(true)
-    preloader.src = fullResSrc
+    const FULL_RES_PRELOAD_DELAY_MS = 400
+    let preloader: HTMLImageElement | null = null
+    const timer = window.setTimeout(() => {
+      preloader = new Image()
+      preloader.onload = () => setUsingFullRes(true)
+      preloader.src = fullResSrc
+    }, FULL_RES_PRELOAD_DELAY_MS)
+
     return () => {
-      preloader.onload = null
+      window.clearTimeout(timer)
+      if (preloader) preloader.onload = null
     }
   }, [photo.id, fullResSrc])