Why extending the War of 1812 would not require a new British deployment

If the War of 1812 continued, how long would Britain need to move enough naval force against the United States?

Little additional time; the Royal Navy already had sufficient forces in theatre and could reinforce if American building continued.

The Royal Navy did not need years after the peace to assemble a decisive North American force. The necessary deployment was broadly in place by the end of the War of 1812. If the United States sustained its navy and funded projected first-rate ships, Britain could reinforce further. The limiting question is therefore American political and construction endurance, not Britain's ability to move a fleet across the Atlantic.