That's right, it's using a ton of space. We are currently working on a new protocol extension for SSB targeted at solving exactly this. Here's a presentation from some months ago, https://www.youtube.com/watch?v=LKr208wpr6Y , although our designs have changed a bit during implementation. See also https://github.com/ssb-ngi-pointer/ssb-meta-feeds-spec
We're building this under a grant from the EU Commission, NGI Pointer, read more about it here https://www.manyver.se/blog/2020-10-update
We're almost finished with a proof of concept of meta feeds for partial replication, and we're working on compiling statistics on how much will it reduce the total payload sizes during replication. For that purpose we built a network simulator to simulate replication at scale: https://github.com/ssb-ngi-pointer/netsim/
If you want to remove it i first recommend making a backup of the 'secret' file, located in that folder, as it contains your private key, in case you ever want to use that identity again. if you do delete that file you will not be able to add new entries to that original identity.