It is a lot and this is why sub divisions should only happen will after launch and the network grows. Then its simpler. The tx manager groups are distributed across the address range evenly so if you had a million exchanges it is likely on a million groups and each group will do very little (signature check). This is one of the hard things to see, but the number of the computations is large but so is the number of groups doing it (like ultra core computing). So early on when the network is small this is an issue but as it grows then less so.