This is due to the site becoming bigger, so slower, and with more people on it
Database size has always been a problem and will always be, hence all my comments about useless background cars, useless quotes, useless thumbnails, etc.
One thing that I'll do to optimize the speed is to have the makes stored in a separate list instead of just a text field. I am not sure that it will help a lot, but it can't be bad anyway.
I'll do something similar for usernames in comments (only problem will be the lost of unregistered usernames in very old comments, which is not very important)