You have many interfaces on your routers and "show running-config" takes a lot of time to generate an output.
Here's a solution that I can provide for you to really increase the speed of the running-config generation: cache the NVGEN process.
NVGEN is used to generate the output of the "show running-config" or "write memory" or "copy system:running-configuration" commands by polling the configuration states of each component and each instance of interfaces and objects.
Once the cache is enabled, the next time you run "show running-config", the cache will be filled. Then, as you run "show running-config", the output will immediately appear.
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