Denoise takes five times longer in batch mode than single image.

Hardware:

• Mac Mini M4 Pro with 24 GB RAM and 16 GPU cores.
• The same issue also occurs on an M1 Pro.
• Lightroom Classic 15.2
• macOS Tahoe 26.3
• RAW ARW files from Sony A1, A9ii and A9i as well as compressed DNG converted files behave similarly.
• GPU acceleration is enabled in Preferences > Performance

Observed behavior with AI Denoise Lightroom Classic 

• Denoising a single image via the Detail panel is very fast: 5–7 seconds.
• When batch-processing even just 2 images, the first image processes quickly (normal speed), but the second image takes 38–40 seconds — about 5× slower.
• In larger batches (e.g., 100 images), the first image remains fast, but all subsequent images (the remaining 99) are consistently slow.
• Creating a preset that applies only Denoise and applying it to a single image results in the slow processing time (~40 seconds).
• Denoising one image quickly, then syncing that setting to another image, is also very slow.

Workaround comparison: Manually scrolling through thumbnails and clicking Denoise on each image individually is an order of magnitude faster than using batch processing, syncing, or presets for multiple images.