Big Amount of <free_space_in_bytes> in Buffer Pool's Database Pages

We were viewing sys.dm_os_buffer_descriptors using below query

select 
 d.[name]										[Database_Name],
 (count(file_id) * 8) / 1024				    [Buffer_Pool_Size_MB],
 sum(cast(free_space_in_bytes as bigint)) / 1024 / 1024		[Free_Space_MB]
from sys.dm_os_buffer_descriptors b
	join sys.databases d on
		b.database_id = d.database_id
group by d.[name]
order by [Buffer_Pool_Size_MB]

And for one of my databases, it shows [Buffer_Pool_Size_MB] = 77325 Megabytes, and [Free_Space_MB] = 15849 Megabytes So its about 20% of space in pages in buffer pool is empty. Seems like a waste of resources Questions: - Is this a problem ? - How can number of free_space_in_bytes be mitigated ? - Any other things to investigate / look at in our situation ?