I also have the same issue, fresh install of kubuntu 15.10, always after booting I get several Warnings.
I use a hdmi monitor.
Last extract from dmesg:

[   44.476443] WARNING: CPU: 0 PID: 768 at /build/linux-26_gwp/linux-4.2.0/drivers/gpu/drm/i915/intel_pm.c:3404 skl_update_other_pipe_wm+0x1de/0x1f0 [i915]()
[   44.476444] WARN_ON(!wm_changed)
[   44.476445] Modules linked in:
[   44.476446]  arc4 rtsx_usb_ms rtsx_usb_sdmmc memstick rtsx_usb bbswitch(OE) bnep hid_logitech_hidpp hid_logitech_dj hid_generic usbhid joydev snd_hda_codec_hdmi uvcvideo i2c_designware_platform acer_wmi sparse_keymap nvidia(POE) i2c_designware_core videobuf2_vmalloc videobuf2_memops videobuf2_core v4l2_common snd_hda_codec_realtek snd_hda_codec_generic videodev media intel_rapl iosf_mbi x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm crct10dif_pclmul crc32_pclmul snd_hda_intel snd_hda_codec snd_hda_core btusb snd_hwdep btrtl snd_pcm btbcm btintel bluetooth snd_seq_midi snd_seq_midi_event snd_rawmidi aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd snd_seq ath10k_pci ath10k_core ath mac80211 snd_seq_device snd_timer idma64 virt_dma snd input_leds serio_raw cfg80211 soundcore
[   44.476472]  mei_me mei intel_lpss_pci shpchp dell_smo8800 tpm_crb wmi intel_lpss_acpi intel_lpss acpi_pad mac_hid parport_pc ppdev lp parport autofs4 uas usb_storage i915 i2c_algo_bit drm_kms_helper r8169 drm ahci mii libahci i2c_hid hid pinctrl_sunrisepoint video pinctrl_intel
[   44.476483] CPU: 0 PID: 768 Comm: Xorg Tainted: P        W  OE   4.2.0-19-generic #23-Ubuntu
[   44.476484] Hardware name: Acer Aspire V5-591G/Usopp_SLS, BIOS V1.03 10/23/2015
[   44.476485]  0000000000000000 00000000f2cd7fef ffff88027509f628 ffffffff817e93f9
[   44.476487]  0000000000000000 ffff88027509f680 ffff88027509f668 ffffffff8107b3d6
[   44.476488]  ffff88027509f730 ffff88027509f7d4 ffff880274872000 ffff880274873000
[   44.476490] Call Trace:
[   44.476493]  [<ffffffff817e93f9>] dump_stack+0x45/0x57
[   44.476496]  [<ffffffff8107b3d6>] warn_slowpath_common+0x86/0xc0
[   44.476498]  [<ffffffff8107b465>] warn_slowpath_fmt+0x55/0x70
[   44.476504]  [<ffffffffc014eb9e>] skl_update_other_pipe_wm+0x1de/0x1f0 [i915]
[   44.476510]  [<ffffffffc014ed6b>] skl_update_wm+0x1bb/0x740 [i915]
[   44.476511]  [<ffffffff810bd110>] ? wake_atomic_t_function+0x60/0x60
[   44.476518]  [<ffffffffc01524be>] intel_update_watermarks+0x1e/0x30 [i915]
[   44.476530]  [<ffffffffc01b9f68>] haswell_crtc_enable+0x488/0xa90 [i915]
[   44.476541]  [<ffffffffc01b6d96>] __intel_set_mode+0x916/0xb60 [i915]
[   44.476551]  [<ffffffffc01bdb06>] intel_crtc_set_config+0x2b6/0x580 [i915]
[   44.476561]  [<ffffffffc0094ef5>] ? drm_mode_create+0x25/0x60 [drm]
[   44.476568]  [<ffffffffc008e4a6>] drm_mode_set_config_internal+0x66/0x100 [drm]
[   44.476575]  [<ffffffffc0092b39>] drm_mode_setcrtc+0x3e9/0x500 [drm]
[   44.476580]  [<ffffffffc0083495>] drm_ioctl+0x125/0x610 [drm]
[   44.476586]  [<ffffffffc0092750>] ? drm_mode_setplane+0x1b0/0x1b0 [drm]
[   44.476589]  [<ffffffff81210a25>] do_vfs_ioctl+0x295/0x480
[   44.476591]  [<ffffffff81087f71>] ? __set_task_blocked+0x41/0xa0
[   44.476592]  [<ffffffff81210c89>] SyS_ioctl+0x79/0x90
[   44.476594]  [<ffffffff8108ab84>] ? SyS_rt_sigprocmask+0x74/0xc0
[   44.476597]  [<ffffffff817f01f2>] entry_SYSCALL_64_fastpath+0x16/0x75
[   44.476598] ---[ end trace 54ca44dc723584de ]---
[   45.796098] vgaarb: this pci device is not a vga device

Do you need additional information?