[ONE General] Genericxx:
Yeah i've tested it, this Option does not solve my issue. Might be a bug in Android 5.02 but even with CM12.1 i still got that Problem whereas CM11 doesn't make this problems while at WiFi. I fiddled out that there seems to be a way to work around this issue if you're rooted. As already mentioned, CM11 hat this "WiFi Optimization" Toggle, which isn't present at Lollipop. I've tinkered with the "WCNSS_qcom_cfg.ini", which is located at "/system/etc/wifi". This file looks like the following:

# This file allows user to override the factory

# defaults for the WLAN Driver

# Enable IMPS or not
gEnableImps=1

# Enable/Disable Idle Scan

gEnableIdleScan=0

# Increase sleep duration (seconds) during IMPS
# 0 implies no periodic wake up from IMPS. Periodic wakeup is
# unnecessary if Idle Scan is disabled.
gImpsModSleepTime=1

#ifdef VENDOR_EDIT
#qiulei add to show the max linkspeed
gReportMaxLinkSpeed=1
#endif /* VENDOR_EDIT */

# Enable BMPS or not
gEnableBmps=1

# Enable suspend or not

# 1: Enable standby, 2: Enable Deep sleep, 3: Enable Mcast/Bcast Filter

gEnableSuspend=3

# Phy Mode (auto, b, g, n, etc)
# Valid values are 0-9, with 0 = Auto, 4 = 11n, 9 = 11ac
gDot11Mode=0

# CSR Roaming Enable(1) Disable(0)

gRoamingTime=0

# Assigned MAC Addresses - This will be used until NV items are in place

# Each byte of MAC address is represented in Hex format as XX

Intf0MacAddress=B0AA33888888
Intf1MacAddress=D4AA33888888
Intf2MacAddress=000AF58989FD

Intf3MacAddress=000AF58989FC

# UAPSD service interval for VO,VI, BE, BK traffic

InfraUapsdVoSrvIntv=0

InfraUapsdViSrvIntv=0

InfraUapsdBeSrvIntv=0

InfraUapsdBkSrvIntv=0

# Flag to allow STA send AddTspec even when ACM is Off
gAddTSWhenACMIsOff=1

# Make 1x1 the default antenna configuration

gNumRxAnt=1

#ifdef VENDOR_EDIT
//qiulei, 2014/01/18, Add sleep scan time to reduce sleep current
#Dynamic Beacon
gEnableDynamicDTIM=3
#endif /* VENDOR_EDIT */

# Beacon filtering frequency (unit in beacon intervals)

gNthBeaconFilter=50

# Enable WAPI or not

# WAPIIsEnabled=0

# Flags to filter Mcast abd Bcast RX packets.

# Value 0: No filtering, 1: Filter all Multicast.

# 2: Filter all Broadcast. 3: Filter all Mcast abd Bcast

McastBcastFilter=3

#Flag to enable HostARPOffload feature or not

hostArpOffload=1

#SoftAP Related Parameters

# AP MAc addr

gAPMacAddr=000AF589dcab

# 802.11n Protection flag

gEnableApProt=1

#Enable OBSS protection

gEnableApOBSSProt=0

#Enable/Disable UAPSD for SoftAP

gEnableApUapsd=1

# Fixed Rate

gFixedRate=0

# Maximum Tx power

# gTxPowerCap=30

# Fragmentation Threshold

# gFragmentationThreshold=2346

# RTS threshold

RTSThreshold=2347

# Intra-BSS forward

gDisableIntraBssFwd=0

# WMM Enable/Disable

WmmIsEnabled=0

# 802.11d support
g11dSupportEnabled=1

# CCX Support and fast transition
CcxEnabled=0
FastTransitionEnabled=1
ImplicitQosIsEnabled=0
gNeighborScanTimerPeriod=200

gNeighborLookupThreshold=76
gNeighborReassocThreshold=81

gNeighborScanChannelMinTime=20
gNeighborScanChannelMaxTime=30

# Enable Firmware RSSI monitoring for roaming
gEnableFWRssiMonitoring=1

# Legacy (non-CCX, non-802.11r) Fast Roaming Support
# To enable, set FastRoamEnabled=1
# To disable, set FastRoamEnabled=0
FastRoamEnabled=1

#Check if the AP to which we are roaming is better than current AP in terms of RSSI.
#Checking is disabled if set to Zero.Otherwise it will use this value as to how better
#the RSSI of the new/roamable AP should be for roaming
RoamRssiDiff=3

# SAP Country code

# Default Country Code is 2 bytes, 3rd byte is optional indoor or out door.

# Example

# US Indoor, USI

# Korea Outdoor, KRO

# Japan without optional byte, JP

# France without optional byte, FR

#gAPCntryCode=USI

#Short Guard Interval Enable/disable

gShortGI20Mhz=1

gShortGI40Mhz=1

#Auto Shutdown Value in seconds. A value of 0 means Auto shutoff is disabled

gAPAutoShutOff=0

# SAP auto channel selection configuration

# 0 = disable auto channel selection

# 1 = enable auto channel selection, channel provided by supplicant will be ignored

gApAutoChannelSelection=0

# Listen Energy Detect Mode Configuration

# Valid values 0-128

# 128 means disable Energy Detect feature

# 0-9 are threshold code and 7 is recommended value from system if feature is to be enabled.

# 10-128 are reserved.

# The EDET threshold mapping is as follows in 3dB step:

# 0 = -60 dBm

# 1 = -63 dBm

# 2 = -66 dBm

# ...

# 7 = -81 dBm

# 8 = -84 dBm

# 9 = -87 dBm

# Note: Any of these settings are valid. Setting 0 would yield the highest power saving (in a noisy environment) at the cost of more range. The range impact is approximately #calculated as:

#

# Range Loss (dB) = EDET threshold level (dBm) + 97 dBm.

#

gEnablePhyAgcListenMode=128

#Preferred channel to start BT AMP AP mode (0 means, any channel)

BtAmpPreferredChannel=0

#Preferred band (both or 2.4 only or 5 only)

BandCapability=0

#Beacon Early Termination (1 = enable the BET feature, 0 = disable)

enableBeaconEarlyTermination=1

beaconEarlyTerminationWakeInterval=11

#Bluetooth Alternate Mac Phy (1 = enable the BT AMP feature, 0 = disable)

gEnableBtAmp=0

#SOFTAP Channel Range selection

gAPChannelSelectStartChannel=1

gAPChannelSelectEndChannel=11

#SOFTAP Channel Range selection Operating band

# 0:2.4GHZ 1: LOW-5GHZ 2:MID-5GHZ 3:HIGH-5GHZ 4: 4.9HZ BAND

gAPChannelSelectOperatingBand=0

#Channel Bonding
gChannelBondingMode5GHz=1

#Enable Keep alive with non-zero period value
#ifndef VENDOR_EDIT
#qiulei remove for wifi connecting
#gStaKeepAlivePeriod=30
#endif /* VENDOR_EDIT */

#AP LINK MONITOR TIMEOUT is used for both SAP and GO mode.
#It is used to change the frequency of keep alive packets in the AP Link Monitor period which is by
#default 20s. Currently the keep alive packets are sent as an interval of 3s but after this change
#the keep alive packet frequency can be changed.

#gApLinkMonitorPeriod = 3

#If set will start with active scan after driver load, otherwise will start with

#passive scan to find out the domain

#gEnableBypass11d=1

#If set to 0, will not scan DFS channels

gEnableDFSChnlScan=1

gVhtChannelWidth=2
gEnableLogp=1

# Enable Automatic Tx Power control

gEnableAutomaticTxPowerControl=1

# 0 for OLPC 1 for CLPC and SCPC
gEnableCloseLoop=1

#Data Inactivity Timeout when in powersave (in ms)
gDataInactivityTimeout=200

# VHT Tx/Rx MCS values
# Valid values are 0,1,2. If commented out, the default value is 0.
# 0=MCS0-7, 1=MCS0-8, 2=MCS0-9
gVhtRxMCS=2
gVhtTxMCS=2

gEnableLpwrImgTransition=1

# Enable Tx beamforming
gTxBFEnable=1
gActiveMaxChannelTime=60
gActiveMinChannelTime=40

# Enable Tx LDPC
#gTxLdpcEnable = 1 for HT mode, 2 for VHT mode,3 for both HT and VHT
gTxLdpcEnable=3

# Oxygen network (prop IE for IBSS)
gEnableOxygenNwk=0

#FlexConnect Power Factor
#Default is set to 0 (disable)
gFlexConnectPowerFactor=0

# Maximum channel time in msec
gMaxMediumTime=5480

# 802.11K support
gRrmEnable=1
gRrmOperChanMax=8
gRrmNonOperChanMax=8
gRrmRandIntvl=100

gEnableTDLSSupport=1
gEnableTDLSImplicitTrigger=1
gTDLSExternalControl=1
gTDLSTxStatsPeriod=500
gTDLSTxPacketThreshold=10
gTDLSDiscoveryPeriod=20000
gTDLSMaxDiscoveryAttempt=5
gTDLSIdleTimeout=40000
gTDLSRssiHysteresis=100
gTDLSRSSITriggerThreshold=-60
gTDLSIdlePacketThreshold=5
gTDLSRSSITeardownThreshold=-70

END

# Note: Configuration parser would not read anything past the END marker

After i have edited the following line

McastBcastFilter=3

and changed it to

McastBcastFilter=0

my device is now again able to wake up from incoming notifications instantly while on WiFi. This seems to be a workaround which really fixes my issue, but at the cost of battery saving.

Edit: My fault. Exchanged gEnableSuspend with McastBcastFilter. Fiddeling with gEnableSuspend makes device won't go into deep sleep