Panda3D Manual: Performance Issue: Too Many Text Updates

If you are using the TextNode or OnscreenText (or similar) interfaces, and you have large chunks of text changing every frame, you might find it to be a big performance hit. Panda3D does a lot of work to assemble the text, so you will want to minimize unnecessary calls to setText() or related functions that force the text to be recomputed.

On the other hand, if you really want to change your text frequently, you can try putting this in your Config.prc file:
text-flatten 0

this will remove the call to flattenStrong() within the text generation process. Changing the text will be much faster, but rendering the resulting text will be slower, since you will be dealing with a lot of meshes in your scene graph.

Panda3D 1.6.0 and later contain a performance optimization that speeds up the text generation. If you have this version, you will also need the following line in your Config.prc, in addition to the text-flatten line, to achieve the same effect (though this is not recommended, for the reason stated above):
text-dynamic-merge 0