database - Optimising Large SQL Server Tables -

i have large table around 50 million rows , 15 columns. whenever read, need columns can't split them. have clustered index on table 4 keys , read data using keys.

but performance still slow, queries fairy simple this

select      countryid, retailerid, fy,      sum(col1), sum(col2),.....sum(col15)  mytable join product p on a.productid = p.id join ...... join ..... join ...... join ..... ....... group countryid, retailerid, fy 

i'm not using in operator or sub queries here on inline functions... know make slow. i've looked @ partitioning not sure that, can performance improvement doing partition?

or there else can do?

i'm using sql server 2012 enterprise edition

please help!

thanks guys, have done using aggregated tables. run job aggregate data overnight has limited number of rows , reports running fine now