No, you cannot record slow-motion videos in 4K resolution on the iPhone 15 Pro. The slow-motion options on the iPhone 15 Pro max out at 1080p resolution at either 120fps or 240fps[1][2][4][5].
While the iPhone 15 Pro can record regular video at up to 4K60 with all of its cameras, the slow-motion mode is limited to 1080p. This is likely due to the enormous file sizes that would result from recording 4K video at 120fps or 240fps[3].
To capture slow-motion footage on the iPhone 15 Pro, open the Camera app, select the "Slo-mo" mode, and tap the record button. You can then adjust the slow-motion section by dragging the white vertical bars beneath the frame viewer[2][4][5].
While 4K 120fps slow-motion recording would be a nice feature, Apple has not yet implemented it on the iPhone 15 Pro. The company tends to add new video capabilities based on market trends rather than pushing the boundaries[3]. For now, you'll have to settle for 1080p slow-motion videos on the iPhone 15 Pro.
Citations:[1] https://www.gsmarena.com/apple_iphone_15_pro_max-review-2618p7.php
[2] https://www.youtube.com/watch?v=BBPMUjPbF6s
[3] https://www.reddit.com/r/iphone/comments/18e4hi1/iphone_15_pro_should_be_able_to_record_120fps_slo/
[4] https://www.youtube.com/watch?v=dGeeYBYSCZ8
[5] https://www.youtube.com/watch?v=G3de7dk2ues