Texture Filter - Mipmapping/VRAM and other flags

One of the programs I am working on had a group of about 25 textured buildings (masked texture) created from 2 different building models which I used copyentity to create further instances with. Using the default settings for the textures (ie no usage of command Texturefilter()) the program ran really slowly (I do have an old PC). However I thought I would see what happened if I turned off mipmapping and load the texture into VRAM using texture filters. The program then ran much faster and the camera motion was very smooth.

Simple question:Why is this so much faster? Would I gain
even more speed if I made all my models textures be loaded
into VRAM and with no mipmapping? Are there any other big speed gains that can be found using other similar functions...

Well, with MipMapping, i believe 3 different versions of the texture are created, so it takes up more VRAM, and might be swapping between system RAM and VRAM more, because your using the force to VRAM flag. Also, if your doing copying from VRAM, the force to VRAM flag speeds things up greatly.

Memory aside, not using mipmapping will slow things down tho.

More about mipmaps:

http://msdn.microsoft.com/archive/default.asp?url=/archive/en-us/directx9_c/directx/graphics/programmingguide/FixedFunction/Textures/filtering/texturefilteringwithmipmaps.asp