This depends on how big your gallery is. Your images should be loading very fast if you have up to about 10 images in the gallery, but beyond that, it is likely that your browser will need some extra time to load the remainder of the images. This is simply because the more images you add to your page, the more images your computer needs to download and display.
In saying this, having a large gallery will NOT affect the loading time of the rest of the page. So you can still place a massive gallery at the beginning of the page to capture your visitor’s attention. However, if a particular visitor has a slow internet download speed they will still be able to browse the rest of the content further down the page while they wait for the gallery to finish loading since text loads much faster than pictures.