We're running a race to Sag A* and of course time is of the essence for pilots trying to get the fastest time. The bad news is there's a certain point where you can't do anything at all to help. It's going to be slow. It has nothing to do with network latency and everything to do with computing power. The route planner works by plotting every course possible using your ship's maxium jump length or most efficient fuel usage in a sphere around your ship. In most cases in colonized space, this takes seconds because systems are spread out. However, in the galactic core, there are 1000x or more systems to map. Check out your nav panel. It lists the 20 closest systems. In colonized space, you might see the 20th system on the list showing 20-30 light years. Near the core, the 20th system might be 3 light years away. Your computer tries to plot the route of every star within whatever radius you tell it, and it grows almost exponentially the closer you get to the core.
The Buckyballers have come up with some remedies to help as you get close, but again they only work to a certain point. After that, your best bet is to plot one jump at a time.
1. Use realistic mode on the galmap.
2. Exit and restart the game. This seems to clear cached routes, but only works up to about 1,000 LY out. After that, you grind.
3. Allow the route plot to reach 99%, then exit the route planner (which may also take a while to do because the CPU is busy.) The computer will remember the route up to 99%, and if you go back to the galmap and select a slightly closer end point to the route, it will complete quickly
4. Plot your jumps in a multiple of your jump range. This was discovered by the current race leader, CMDR Alot. If your jump range is 30 LY, look for stars at 30, 60, 90, 120, 300, 600 light years out, etc and the computer can plot them faster. If your range is 25 LY, look for 25, 50, 75, 100, 150, 200, etc. It requires some math, but Alot reported the effect was reproducible.
Remember, if you plot a route of 1000 LY, your computer has to look at every star within that range to see which ones make the closest route. In the galactic core there are so many stars in that sphere that your computer can't keep up. Anything you can do to reduce the required processing power the better off you will be. But you might also just resign yourself to the fact that getting in and out of the core will take a lot of patience and discipline.
Good luck CMDRs!