Are you rooted? If so you can use the paid version of TB (Titanium Backup) and freeze apps versus uninstalling to help you gain some ram back.
Edited to add.
I don’t believe ram usage is causing your speeds to be low. I’m thinking you can manage it better.
Your download / upload speeds will vary through out the day as how bust the server is you’re trying to test from. Example: once might get better speeds from the server at 12am rather than 8pm.