This is a contradiction.
If you want to change the frame rate speeding up you have to change the frame rate.
You could try to playback a video at 16,000 fps... Why would you need to playback a video to 16,000 fps if no human or living being could notice the difference to let's say 120 fps?
You also need a monster of a computer to playback that among other ...
You can not. You have contradicting parameters.
You need to make some decisions. Either:
Leave your project at 29.97 and drop 1 every 2 frames of your 60fps clip.
Leave your project at 29.97 and use all the frames of the 60 fps clip making it slow-motion 2x.
Change the project speed to 60fps and render twice every frame of the other footage.
Change the ...