Database capacity used by multiline text fields/single line

Hi

Can anyone advise me on the database capacity usage and field length / type.

We have 15m records with 2 multiline text fields containing data, each limited to 2000 characters.

Would we save space by doing either of the following:-

1) Shortening the field length to 400 chars, which is the longest data field length.  Most have about 10-20 chars used.

2) Creating new single-line text fields (limited to 400 chars), moving the data in and deleting the mulitline text fields?

Thanks!