Python Script Tool Startup Performance

I created a series of Python script tools that run in ArcMap 10.2 and noticed that there was significant lag before any code I wrote ran.

As a test, I created a Python script file with no executable code in it. I didn't even import arcpy. Under these conditions, the tool still takes around 25 seconds to run.

I tried enabling/disabling background processing and logging, and neither of these had a noticeable effect.

Does anyone have any suggestions for how to improve script tool startup speed?