2 usbcams on 1 usb bus with 15 fps is possible - how to set frames per second?

Question

root@mercure:/tmp/motion# cd /etc/motion/
root@mercure:/etc/motion# motion
[0] Processing thread 0 - config file /etc/motion/motion.conf
[0] Processing config file thread-envivo1.conf
[0] Unknown config option "hight"
[0] Processing config file thread-envivo2.conf
[0] Unknown config option "hight"
[0] Motion 3.2.12 Started
[0] ffmpeg LIBAVCODEC_BUILD 3474688 LIBAVFORMAT_BUILD 3473920
[0] Thread 1 is from thread-envivo1.conf
[0] Webcam port number 8082 for thread 1 conflicts with thread 0
[0] Webcam feature for thread 1 is disabled.
[0] Thread 2 is from thread-envivo2.conf
[1] Thread 1 started
[2] Thread 2 started
[0] httpd bind(): Address already in use
[0] httpd thread exit
[1] cap.driver: "uvcvideo"
[1] cap.card: "Venus USB2.0 Camera"
[1] cap.bus_info: "usb-0000:00:1d.0-1.1"
[1] cap.capabilities=0x04000001
[1] - VIDEO_CAPTURE
[1] - STREAMING
[1] Config palette index 8 (YU12) doesn't work.
[1] Supported palettes:
[1] 0: YUYV (YUV 4:2:2 (YUYV))
[1] Selected palette YUYV
[1] Test palette YUYV (640x480)
[1] Using palette YUYV (640x480) bytesperlines 1280 sizeimage 614400 colorspace 00000008
[1] found control 0x00980900, "Brightness", range -10,10 
[1]    "Brightness", default 0, current 0
[1] found control 0x00980901, "Contrast", range 0,20 
[1]    "Contrast", default 10, current 10
[1] found control 0x00980902, "Saturation", range 0,10 
[1]    "Saturation", default 4, current 4
[1] found control 0x00980910, "Gamma", range 100,200 
[1]    "Gamma", default 150, current 150
[1] found control 0x00980913, "Gain", range 32,48 
[1]    "Gain", default 34, current 34
[1] mmap information:
[1] frames=4
[1] 0 length=614400
[1] 1 length=614400
[1] 2 length=614400
[1] 3 length=614400
[1] Using V4L2
[1] Resizing pre_capture buffer to 1 items
[2] cap.driver: "uvcvideo"
[2] cap.card: "Venus USB2.0 Camera"
[2] cap.bus_info: "usb-0000:00:1d.0-1.3"
[2] cap.capabilities=0x04000001
[2] - VIDEO_CAPTURE
[2] - STREAMING
[2] Config palette index 8 (YU12) doesn't work.
[2] Supported palettes:
[2] 0: YUYV (YUV 4:2:2 (YUYV))
[2] Selected palette YUYV
[2] Test palette YUYV (640x480)
[2] Using palette YUYV (640x480) bytesperlines 1280 sizeimage 614400 colorspace 00000008
[2] mmap information:
[2] frames=4
[2] 0 length=614400
[2] 1 length=614400
[2] 2 length=614400
[2] 3 length=614400
[2] Error starting stream VIDIOC_STREAMON: No space left on device
[2] ioctl (VIDIOCGCAP): Invalid argument
[2] Could not fetch initial image from camera
[2] Motion continues using width and height from config file(s)
[2] Resizing pre_capture buffer to 1 items
[2] Started stream webcam server in port 8082
[2] File of type 2 saved to: /usr/local/apache2/htdocs/envivo2/webcam2.jpg
[2] File of type 2 saved to: /usr/local/apache2/htdocs/envivo2/webcam2.jpg
[1] File of type 2 saved to: /usr/local/apache2/htdocs/envivo1/webcam2.jpg
[2] Retrying until successful connection with camera
[2] cap.driver: "uvcvideo"
[2] cap.card: "Venus USB2.0 Camera"
[2] cap.bus_info: "usb-0000:00:1d.0-1.3"
[2] cap.capabilities=0x04000001
[2] - VIDEO_CAPTURE
[2] - STREAMING
[2] Error selecting input 0 VIDIOC_S_INPUT: Device or resource busy
[2] ioctl (VIDIOCGCAP): Invalid argument
[2] File of type 2 saved to: /usr/local/apache2/htdocs/envivo2/webcam2.jpg
[1] File of type 2 saved to: /usr/local/apache2/htdocs/envivo1/webcam2.jpg
[2] File of type 2 saved to: /usr/local/apache2/htdocs/envivo2/webcam2.jpg
[1] File of type 2 saved to: /usr/local/apache2/htdocs/envivo1/webcam2.jpg
^C[1] Thread exiting
[1] Calling vid_close() from motion_cleanup
[1] Closing video device /dev/video1
[2] Thread exiting
[0] Motion terminating
root@mercure:/etc/motion# 

Environment

Answer