The Scout Android application size varies upon phone model and OS version. The size is roughly about 18mb, which is a compressed file. The Android OS controls how large the files actually become once installed.
If you're finding yourself having issues with this specific error, you must delete an application or anything saved on your handset which may be taking a lot of memory. Telenav Inc. does not suggest any specific app to delete and understands if a customer chooses to not delete other apps to have Scout.
Again, this is not a Scout issue, but rather an issue with the device memory.