Encrypting and decrypting are complex operations that requires a lot from the hardware. The resources needed to encrypt and decrypt is proportionally correlated with the amount of files you’re encrypting and decrypting.
That said, there are some alternatives
Encrypt the whole filesystem
Encrypt only your home folder
Encrypt only the files you wanna
There is an app, Vaults, that allows you to create vaults to easily encrypt and decrypt folders. Take a look on this app