Yes, you may bring in your hard-coded GA tags inside GA extension in Adobe Launch. You might need to work with an implementation consultant to make sure the configuration is done correctly so that you have the same data collected as from hard-coded tag from the extension.
Moving hard code tag to GA launch ext is a good idea, not sure if this will help reduce page load time though. It will certainly help mange GA tag better. If installed correctly you should not see any impact over data collection.