Gotcha.
You had NO data or select statement in your main report and you are NOT linking the sub reports to the main report in any way.
Once you addanything to the Main report it will draw one detail row per record from the source data making your sub reports repeat over and over and kill your performance.
Since you are not linking these, move your sub reports to the Report Footer or Header. Add one report per header or footer section (insert as many new extra footers or headers as you need).
Suppress your details section.