2 Sparse Bundles?

Only one sparsebundle is used per computer.

It is pretty unusual for TM to create a new backup without wiping the old one. Unless you made some major change to the computer like change hard disk.. in which case it will start over.. because the new install has different UUID and hence backup now has a different UUID.

You can discover such details using tmutil from the command line.

Suggest you read the man page first.

Delete the older one as it is no longer relevant .. unless you know there are files in there you need.. in which case you should archive the TC first to USB drive.. and then delete the sparsebundle.

I think you will do a lot better.. archive the whole lot.. and start over with erase of the TC disk.

If you are on Sierra or High Sierra.. then Time Machine is having loads of issues to network drives.

You must NOT use any Anti-virus software.. extra security software.. and almost anything with up in the name.. cleanup speedup.. memory recovery etc.. ie adware.

And TM is now sufficiently unreliable as to require a change from using it on network to limiting it to local drives only.. ie USB plugged directly into the computer.

And even scrub TM altogether and run Carbon Copy Cloner etc.. as a far more reliable backup.

Slow backup is a bit different issue to what you posted..

But loads of people find everything speeds up dramatically after a full network reboot.

Of course if you use wireless then all sorts of things depend on the wireless speed. There is nothing to fix wireless issues.. like NOT using wireless.. change over to wired connections for decent reliability and speed.

But I do encourage people for now OFF TM to network drives.. from Sierra it has become too unreliable.. partly at least due to increased security that Apple enabled to prevent ransomware being able to encrypt your backup. If the computer cannot reach the backup then it is safe I guess is the rationale.