As of today, website assets are automatically distributed via a global CDN (Content Delivery Network). This means that the load time of images, videos, etc. will be similar in San Francisco, New York, London, Frankfurt, Singapore or Tokyo.
Good to know:
This only affects visitors who are not logged in. So it affects your website's visitors but not your own pageloads when editing your website. (Which is not an issue as it will be cached in your browser anyway.)
The first time images, etc. are accessed, they are not yet cached on the "edge server", so the speed gain will only show from the second access. This is called cache warm-up. It doesn't matter who loads it. If one visitors clicks around on your website from Japan, it will be fast for everyone in Japan.