Study up on rendering and formats. The default for the Render Cue and output module is lossless which is not compressed very much and is not designed for playback or distribution. To render deliverable files you should use the Adobe Meida Encoder. Drag your "lossless" file into the AME and choose one of the standard h.264 presets that match your project frame rate and frame size. I suggest the YouTube presets.
Anyone doing any kind of video production owes it to themselves to spend at least a couple of hours learning about video formats, compression and standards. Basically, if you are using a composition setting or render settings that say "custom" you have a more than 90% chance that you are doing something wrong. The video standard for almost all production is HDTV 1920 X 1080 @ 29.97 fps or 25 fps if you live in a country that has 50 hz electrical service (Europe - PAL). The most common delivery format is mp4 using h.264 compression. If you use anything else you had better know exactly what you are doing.