I haven’t any experience with flight plans that large, but it could help to switch off GPS, if you can handle that in-flight (?)… and/or put map off when it is not really needed… suppose while you’re flying, the sim needs to locate where you are in the flight plan. If it has to search 1600 entries every time GPS is refreshed… maybe that will slow down performance.
Great plan ! please keep this forum informed if you find something really great…