Greetings Lucian,
These are large numbers, although as the number of FLs in a single Plant can easily go up to hundreds of thousands, it is not unimaginable if you have dozens of Plants in the system. I imagine that this is an implementation across a large number of locations and plants, so good templates and rules for master data maintenance are key.
As far as performance goes, I expect that your system is sized appropriately, given that there will be a vast amount of data processed in the other domains as well (such as MM or FI). As Peter Atkin suggests above, speak to your BASIS team if you have concerns.