What type of videos are you doing on your 2nd channel? If you feel that your audience on your main channel will also have an interest un the videos on your 2nd channel - let them know in your uploads..maybe before the intro..or after the intro
I agree with doing collabs. But seriously don't stress too much about the rate that your growing. It is important to always be willing to improve your channel for one. Also it really does take quit some time to build up a good channel.