I have had to deal with this issue before.
This is hard because it's about making your game more efficient, and you really need to know the structure to do this well.
You have identified "Monsters with animations" as the worst performing loads.
1. Consider the Enhanced Animation plugin. This will allow you to load animations from files separately from the model data. Have the DBO files not contain animation at all. It will also provide you with better animation transitions.
2. Use DBO/DDS formats. You have mentioned this. It is fastest.
3. Never use model baked in textures. You have mentioned this.
4. Cache as much as you can, be as clever as possible. You mentioned ram goes through the roof. You should take another look at that, it's hard to see how you could be eating too much ram.
5. Keep track of every object/image number and their paths you load. If the identical one is to be loaded, clone the object instead, and/or point to the existing image. Keep track of how many times they are being used so you can delete them if no longer needed.
6. Without multi-threading support it's somewhat impossible to properly stream in assets. You could create a convoluted system that suspends the monster in some form in a deffered manner off screen, where you load the model, textures, and other assets, with screen draws in between. You'd probably get a little less screen lag doing this. Basically a monster loader manager.
7. You can extend things and build sophisticated system that manages the load in of assets. Keep a list of everything waiting to be loaded. Keep track of how much time has been taken since last frame draw. If too much time was taken stop, and pickup again when the next main loop comes around. You could mitigate lag spikes using this approach.
You definitely need to figure out clever ways to cache what you can. Depending on how your game is structured you might be able to predict things to cache allowing you to reduce the amount of caching needed. This is the hard part that isn't straight forward that turns you from being a student into a megamind.