Ideally, a swap partition should always be on a secondary physical device than your home directory. Or anything else, if possible, as there will be high i/o during times of high memory activity and memory/swap maintenance.
Your bottleneck is exacerbated more by the excessive overhead of on-the-fly decryption activity on the same physical device
All of this can be avoided by eliminating swap, which isn’t necessary if you have sufficient RAM.