Using multisite the subdomains are all loading very slow

We are using a Multisite format with the Gameday Theme. Our main site,, loads fine. But the subdomains * (example ( are loading slowly. This could be a result of multiple polls that are being run using Crowdsignal, or maybe something else. We need to find a way to speed up the load times as well as the load times for the wp-admin backend, as the subdomains there are also loading slow. I have installed Hummingbird and tried to optimize, but doesn't seem to help. Please advise