Hmmm. Not sure what went wrong. A few weeks ago, I deleted a sparesbundle file for an old Mac that we no longer use and it took only 3-4 minutes to delete the file, which was about 100 GB of data. I was using a Mac running El Capitan to delete the file.
As far as partitioning the Time Capsule drive, this is not practical for most users, since Disk Utility does not have the ability to partition a network drive like a Time Capsule.
In theory, it might still be possible to pull the hard drive out of the Time Capsule, connect it to a SATA to USB converter or caddy, connect the caddy directly to the USB port on your Mac, and then try to partition the drive that way. Then, you'll have to reinstall the drive back in the Time Capsule and hope that things will work.
I've done this, but used a new larger 4 TB drive and partitioned it before I pulled the old drive out of the Time Capsule, which was about 4 years old at the time.
Not an easy project, and somewhat of a challenge even for a dedicated do-it-yourself type of person......as the older Time Capsule was not designed for easy maintenance. If you have a tech pull the drive from your Mac, it will probably cost more that simply buying another Time Capsule and then using one TC per Mac to back up.