Minimize or turn off panel preview thumbnails
Each time you change the document, Photoshop updates all the thumbnails visible in the Layers and Channels panels. This update can affect responsiveness when rapidly painting, moving, or nudging layers. The more thumbnails are visible, the greater this effect.
To minimize or disable thumbnail previews in these panels, click Channels, Layers, or Paths panel and choose Panel Options. In the Thumbnail Size area, select a smaller thumbnail size or choose None, and then click OK.