The major factor in video file size is the bitrate, resolution and frame rate (fps). Generally, overall quality improves with higher bit-rates, which also results the larger video file size.
Quick tips for reducing your movie size:
The larger the screen resolution with which you record, the more information is recorded, and the larger movie size will be. So try to record at the lowest screen resolution possible.
Lower the video bitrate, if the video file is compressed at higher bitrate, the higher video quality and larger file size will be. And vice versa.(You can set it in Options->Screen Recording->Output Video Format->Bitrate)
If possible, avoid recording pictures, photos or animations as these will boost file size significantly.
Use plain desktop wallpaper, as complex wallpapers can add literally megabytes to your final file size.
And the key point to remember: file size is mainly affected by movie content, not movie running length