Assuming that you've optimised the pictures (for example don't use a 2048 x 2048 image then scale it down to 50 x 50) the speed should be reasonable.
The rate it renders depends on the speed your PC reads it off of the drive, the rate java works at and the browser render engine.
A fast PC will make it appear faster, sunject to the limitations of the browser engine.
I tried one module on some PCs at work,
(a)x8 3.3Gig cores, 4Gig DDR3 & nvidia Quadro FX3700
(b)x8 3.3Gig cores, 128gig RAM & quadro 3800.
So a fair bit of power to play with (we have some serious toys)these will read 256Gb of image data (8 images) and draw it on screen in under a second. It was plenty fast enough but still not 'instant' .. That's the java and browser engines slowing it down