journal-upload (217) creates a lot of log entries, which are essentially verbose libcurl output. This might be useful in case of debugging connection issues, but spams a central log with a lot of noise and puts some significant load on the sender (an RasPi in that case). The relevant place might be in src/journal-remote/journal-upload.c at line 246 :
               /* enable verbose for easier tracing */
                easy_setopt(curl, CURLOPT_VERBOSE, 1L, LOG_WARNING, );