I had the same issue where selecting the custom Tool Palettes after importing them were running really slow about 2 minutes to load each one.
We are using C3D 2016, I have my custom company's exported Tool Palettes Files (.XTP) and AutoCAD drawing files for each tool palette containing everything I put on that particular Tool Palette such as blocks, hatching, multileaders, etc. located here:
L:\CADD Std\Tool Palettes\_Share Palettes
this is where I update all the AutoCAD drawings when I have something to add to that Tool Palette.
To make the Tool Palettes run faster, I changed the users Options for Tool Palettes File Locations to:
C:\Users\user name\AppData\Roaming\Autodesk\C3D 2016\enu\Support\ToolPalette\Palettes
The default options tool palette file locations only goes to the ToolPalette folder in blue above.
I added the Palettes folder at the end of this string - ----- this is where the .ATC files are for each user.
Then I imported the custom tool palettes from the L:\CADD Std\Tool Palettes\_Share Palettes, and now it runs fast switching to the different tool palettes.
Civil 3D 2016 SP2
"We ran into this problem with very decent machines and local custom palettes. To ensure it was not a graphics issue, we went into 3DCONFIG. We toggled hardware accel. off, ok'ed out of 3DCONFIG, went back in and turned Hardware Accel back on. This instantly made a differnce and the palettes are completely responsive at this point."
I found the solutions above works with my issues with custom tool palettes switching lags.
While this is an old topic, maybe this will help someone. As others have said, the fix for making the tool palette load faster was to add ToolPallette\Palettes folder to the top of the list in the Tool Palettes File Location tree. Just a note about that, don't do this on a fresh install until after the tool palettes have been loaded. I thought since I was going to do it anyway on a fresh install, I would just do it while I was doing some of the other stuff we always do, but it doesn't work until after you install your Tool Palettes. I chased that around for a while, because if you do it before, it doesn't save the Tool Palettes after you close Autocad. At least in my experience.
As for the blocks loading slowly, come to find out, is an Autocad issue, always has been. There where other issues as well, like drawings taking forever to open, saving and stuff. There is a hotfix for this, and it made this 1,000 times better. Our whole office was having this issue, 2013 and 2016. Finally fed up, we got with our Autocad rep, and he pointed this out, said try this. It didn't work on the 2013's, but did on the 2016's. We are all on 2016 now anyways, but there was supposed to be a fix for 2013. Since it didn't work, they said to try it on a fresh install, which we never tried. It is a .dbx file, one simple file replacement. Works like a champ.