Remove "historical" objects from repository to save place

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Is it possible to conserve space by removing old versions? Let's say I am not 
interested in kernel versions before 2.6.15 - is it possible to remove them 
from repository cloned from one of "official" ones (Linus or stable).

Description of git-prune suggests that it may be possible by removing tags 
from refs/tags; OTOH I may have commit chain that will prevent them. Also 
won't those tags come back after git fetch --tags?

TIA

- -andrey
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