It's just to ask ips if they could improve the load time of member's background image (hover image on root forum) because it take about 3 second to load, it is very slow and let this feature a little useless as members won't wait 3 or 5 second just to know what image have been set by someone.

This is almost entirely related to how fast the client's internet speed is, how close the server is and the speed to the server from the client. IPS essentially just serves an image - there aren't many optimizations to be done. 

Yeah this sort of thing is up to the webmaster. You could use a CDN to store the image files on servers closer to the users. Leverage caching so that the users only have to load the image once. Implement image optomisation to decrease the size of the image and therefore have it load faster.