If it has many images, it will definitely slow down page loading. In a typical web page, the actual text, including the HTML code, might be, say 20 - 40 KB. But a high-resolution photograph could be a megabyte or more. Put two or three such photos on a page, and that means a lot of extra data that has to be downloaded.
One solution is to reduce the size and the resolution of the photo. A low-end camera might take pictures at 2816 x 2112. These will typically be 1 - 1.5 MB. But if you reduce the size to 800 x 600, and reduce the "quality" to, say, 70%, the result might be less the 100 KB - with no noticeable drop in the qaulity of the image on the page. That's a really big saving, which will translate itself into much fast load times.
As to whether the images will lead to poor navigation, the short answer is no. Image sizes and page load times do not directly affect the user's ability to navigate - unless the visitor gets so bored with waiting for the page to load that he abandons the site altogether.