ok, it's not definitely solved, but i have some green shards, and the timeout/retry seems to be working (note timestamps):

06:42:14 [DEBUG] urllib3.connectionpool:pid=3921: Starting new HTTPS connection (1): <http://pypi.org:443|pypi.org:443>
06:42:29 [DEBUG] urllib3.util.retry:pid=3921: Incremented Retry for (url='/simple/pantsbuild-pants-contrib-awslambda-python/'): Retry(total=4, connect=None, read=None, redirect=None, status=None)
06:42:29 [WARN] Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ReadTimeoutError("HTTPSConnectionPool(host='<http://pypi.org|pypi.org>', port=443): Read timed out. (read timeout=15)",)': /simple/pantsbuild-pants-contrib-awslambda-python/
06:42:29 [DEBUG] urllib3.connectionpool:pid=3921: Starting new HTTPS connection (2): <http://pypi.org:443|pypi.org:443>
06:42:29 [DEBUG] urllib3.connectionpool:pid=3921: <https://pypi.org:443> "HEAD /simple/pantsbuild-pants-contrib-awslambda-python/ HTTP/1.1" 200 0