Slow animation


I am relatively experienced in Toon Boom Studio 5.0, and have created two rather large highly detailed animations using this software. My technique is to create png images in photoshop, and export them into toon boom, creating different layers for each body part, or prop that will move in the animation. I then manipulate each part in a similar fashion to cut-out animation. A recent project I am working on appears to be rather slow, and awful if trying to preview a piece of animation I have just completed (via the html player, or ‘preview movie’ in the toolbar area). The project is in full colour, and will be around 3 minutes in length. I created a previous project of the same length, only this was in black & white. I had no issues with this project, could it be because it was indeed in black and white (less memory)? I noticed that some png files for the latest project for some reason had saved in MB from photoshop. I have replaced all these imports with KB png files, seems to have improved slightly, but not brilliantly (considering I am only 30 seconds into animating this latest project). The soundtrack I have been working too, I have also replaced this with a soundtrack in KB (adjusted the bitrate to a much lower quality), but still not brilliant. What could be going wrong, why is this project running so slow, and previous projects were fine? There is more detail as stated with this latest projects artwork, but nevertheless as stated, they are all kb files. Any response would be greatly appreciated. If you need more information or screenshots please let me know